That One Level / Bloons Tower Defense

Ninja Kiwi has a lot of fun with their track design in their beloved Bloons Tower Defense series; that much is clear. But some of these tracks can mess up your day, and a few of them are explicitly designed to mess up your day, such as the Expert/Extreme tracks. Here are some of the best examples:

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BTD4:

Tracks

• Bloons Tower Defense 4 (Deluxe):
  • Monkey Vs. Bloons is a remake of the pool levels from Plants vs. Zombies. As a result, it has six paths that go straight to the house without any bending or turning except at the end. At least this track has water for Monkey Buccaneers.
  • The Triangle of Insanity takes the form of Penrose Triangle. It has three entrances that double as exits.
  • The Ant Hill track. It has one entrance, but the bloons go around a loop near that entrance before heading down one of 4 separate exit paths. It has 2 puddles of water, but they only go between the 1st, 2nd and 3rd paths, none between the 3rd and 4th paths. There is also a challenge on the Flash version that requires you to complete the track on Hard without leaking any bloon.

BTD5:

General

• One of the last five levels in Hard difficulty (specifically, Round 82) involves a rush of BFBs and MOABs... and it starts off with a rush of camo regen bloons topped with a train of BFBs. Fun!

Tracks

• The Bloontonium Lab has three very short paths that form the hazard symbol. This track also doesn't have any water on it, so Monkey Buccaneers are out of the question unless you get a Portable Lake. Worst of all, its status as an Extreme difficulty map means you can't even save the game to make it easier.
• Clock's an extremely awkward track to play on, as the path changes as the clock's hands move, which changes every round.
• Special mention goes to the downright sadistic Down The Drain (with four short paths). And god forbid you play on Impoppable Difficulty... The only thing that can save it is the fact you can do Save Scumming because it's an Expert track, rather then Extreme.
• Wish to achieve 100% completion or just earn many Awesome Points? Get ready to cry; Tar Pits has five separate paths, and the bloons will reverse direction every 2 rounds. To boot, it's also Extreme, so you can't even save the game at all on Flash version. It's hard enough, the developers said the map is impossible without agents, premiums, specialties, or free towers on Hard and higher.
• Crypt Keeper has one entrance... But by the end, it splits into ten separate exits to defend, the most exits seen in the series. Note that this is an Advanced map. However, it can be made much easier if you play in reverse mode, where you have ten entrances and one exit.
• Death Valley has two paths, each separated by a giant wall. One path is fairly manageable, while the other is the shortest in the game. God forbid if a Z.O.M.G. spawns on the path, especially on round 85 on Impoppable Difficulty...
• Double Double Cross. It has four entrances and exits, each being very short. To rub salt in the wounds, The entrances are also the exits, so don't even think of using Spike Factories. It's not the hardest expert map, but it definitely stands out as one of the worst.

BTD6:

Tracks

• Chutes is rated as an Intermediate map but is harder than some Advanced maps. It consists of two relatively short paths with only a small area of overlap. Each round, bloons alternate between paths, meaning that if you want to build towers outside of that small crossover zone, they'll only be useful half the time.
• Bazaar gained some notoriety as well despite being Intermediate. Take Infernal, add some line of sight-blocking trucks onto the track, move the water so Subs and Boats are not very useful, and make the paths alternate in opposite direction, and you'll get a map that is way harder than most Advanced maps and can even surpass Chutes in difficulty. A main annoyance factor was that the map appears to have enough space to place towers in the center, but this space is actually rather small and can only fit anything as small as Dart Monkeys. Its difficulty was rather hard that Ninja Kiwi nerfed the track on version 23.0 by increasing the space to place towers in the center.
• Speaking of Non-Indicative Difficulty: Geared is an Advanced map, but its difficulty is higher than half of the expert maps. It consists in a single path doing a half-circle around a huge gear (the only possible tower spot). While the difficulty from such a map would already be reasonable, this is without counting on the level's gimmick: every round, the big gear rotates clockwise by 1/8 of a turn, and all towers on it with it. This means that, on some rounds, your towers will be useless as they won't be able to reach the track. The solution is to use global range towers such as helicopters or aces, but these towers tend to be rather expensive, making the early game a true challenge.
  • Have fun playing Geared on Alternate-Bloons-Rounds mode. Camos, Leads, and MOAB bloons come far too fast and tough to be defeated without some seriously impressive playing.
  • It's even worse on Apopalypse mode, as with the lack of end of round cash in addition to the gear spinning the instant another round starts, managing your defense will be very hard. Good luck even being able to afford a Heli-Pilot.
• X Factor is another map with Non-Indicative Difficulty, being harder than many Expert maps despite its Advanced status. The track consists of an X made of squiggly, looping lines, making the bloons hard to hit for many towers. Bloons will come down two of the X's lines, but the lines they come down change every round, making the early game quite a challenge. You also have to remove an expensive obstacle to be able to place a tower in the X's center.
• The "True Expert" maps are the game's answer to extreme maps from previous titles (as the game doesn't officially have any extreme-difficulty maps). They all share a sadistic level of difficulty from having at least four short paths, many obstacles, or even both.
  • #Ouch is, in essence, this game's answer to Main Street from BTD5, but with a twist; there's double the lanes, all of them going directly horizontal or vertical of one another, and they alternate all the time. Not helping is that the center of the map has a bit of water, which you have to pay to remove... and with it, you remove all of the water on the map. For a time, it was deemed outright impossible to clear the map in CHIMPS (dubbed "#Couch" by the devs and fanbase)—it is doable, but it took multiple updates after the game released to even prove it, and it is still very much an uphill battle.
  • Muddy Puddles is yet another Expert track that was thought to be impossible to beat CHIMPS (with the humorous nickname of "Cuddles" used amongst fans and the devs to describe such a feat). 4 paths, all very short, with a slight wave to them; and of course, the titular puddles, which do serve as water, but are also some nasty chokepoints. It has since been made easier and has been overshadowed by... well, you can see the next entry, but even now it is quite the formidable track.
  • Bloody Puddles is an even harder remake of the aforementioned Muddy Puddles, and is generally considered the hardest map in BTD6 bar none. Compared to its predecessor, it add a fifth path for bloons which, instead of using only one of the paths, now use two at the same time, one stream towards the top and one towards the bottom in a mirror fashion. As a result, on some rounds, you'll be dealing with bloons almost half a screen apart! There's also a jeep that blocks your sight, and if you pay to have it removed? The chinook that tries to carry it crashes, forcing you to pay for that to be removed, before you can actually get rid of it. Worse, the paths are even shorter than in Muddy Puddles, making them the tied fifth shortest paths in the game behind Blon's path, Erosion's post-90 path and the two vertical paths of #Ouch. That map is so difficult that it took nearly five months and one nerf (reducing the hitbox of the jeep in version 14.0) for Bloons Tower Defense veteran Jajajosh to find a way to Black Border it.
  • Quad is full of short, interconnecting paths, it's very easy to lose track of which Bloons are a second away from the exit and which have just entered. There's water that's too far away from the main track to be efficient, and no tower can efficiently hit all paths at once.
  • Ravine quickly gained infamy due to being fully impossible to beat on CHIMPS at launch. The map starts out with two entrances that split off into four exits. However, there are numerous bridges and trees in the way that blocks the sight of towers, and there is not a lot of space to place towers. No tower is able to counter all of the lanes at once, and especially the leftmost lane is extremely short. The water on the map is basically useless as well, since the line of sight for water towers are blocked when placed there. You better have plenty of powers if you want to even think about beating even Impoppable or Half Cash on this map. As for CHIMPS, well, the map wasn't really nerfed per se, but an update allowed you to click the sword 30 times to dislodge it and pop exactly one red bloon, the one that cannot be popped using 3 dart monkeys, on round 7. For the rest, you'll have to do it the hard way.
  • Dark Dungeons. Four paths that are pretty much all divided up into three different sections blocked by line of sight, and none of the paths really intersect. All the paths are very short too, and there is only a small pond at the bottom right of the map. There is also an Easter Egg where you can activate the statue, but for its cost, it's mostly a Useless Useful Spell that won't do a lot against the bloons.
• Blons, a hidden track available through the challenge editor. It's a slightly modified version of Slons, a joke map designed by a fan, consisting of a minuscule corner track and nothing else. While somewhat easier than it looks (most of the hardest maps are hard because of splitting/changing paths and sight-blockers, while Blons has no gimmicks), it's still the shortest map in the game and there isn't much space to place towers around the track, meaning that only specific defenses can take everything out fast enough. Whilst not really that bad on its own if you're doing a Self-Imposed Challenge in the editor due to the ability to reload last round, it can be a pain on Advanced Challenges, especially if the bloon speed is increased.
• Primary Monkeys Only, being on Easy difficulty, should be easy, right? Unfortunately, Flooded Valley on Primary Only is considered the hardest map to beat on this mode without powers. Only three Primary upgrades total (Blade Maelstrom ability and a bottom path Dart Monkey on a lower rock, albeit both with great difficulty, and the MOAB Assassin Ability can also target the round 40 MOAB) can see up the map's characteristic dam, leaving players to be forced to rely on a singular Hero Unit (either Adora, who can see up the dam, or Brickell, the only naval hero) to deal literally all their damage. Prepare to leak a lot.
• Erosion is another difficult map. The map starts with a short line at the bottom left corner, then every 18 rounds, some part of the ice will break, causing all the land towers standing on the ice to be sold (and naturally, this will not get you the money back in CHIMPS), as well as changing the path according to the coast's location. The erosion ends at round 90, the path becomes very short again and the remaining land masses are even less than of a flooded Flooded Valley (which is an Expert map, but is likely easier than this Advanced map)! Since you can't build Heli Pilots or Monkey Aces on the small land at the top, you'll have to rely on other kinds of permanent DPS, mainly water towers and land towers with infinite range and a small footprint like Psi or Sniper Monkeys, while using relatively cheap temporary land towers to handle early rounds. Whether it's another true expert map is still debatable, but it's definitely harder than many of the Expert maps.

Rounds

Sometimes, no matter what map you're on, it's the rounds that'll give you trouble. Here's a few of those!

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• Round 4 in BTD6 is unusually hard for something that early. It sends a tight clump of Blue Bloons, in a period where your towers do no more than one damage, high pierce towers are slow, and fast towers can only hit a few bloons at once. While you can usually tank it if they leak, this round has been the bane of many no lives lost challengers. It's led to jokes that Impoppable is easier than Hard because it skips straight to round 6.
• Rounds 63, 76, and 78 in BTD6 can be these without heavy bloon popping power, because large amounts of tightly clumped ceramics appear on these levels. Specifically, 63 is three groups of regular ceramics, 76 is an even larger cluster and they're all regrow, and 78 is two large clusters of ceramics and one is all-camo. In Alternate Bloons Rounds, round 76 is Inverted in that it contains 10 B.F.B.s instead of a regrow ceramic rush. Such is Round 63's infamy that there are two special Freeplay rounds in BTD6 based on it. Round 163 changes the relatively tame-sized waves of Leads and Ceramics to immense waves of really fast Camo Regrowth Fortified Leads and Ceramics, respectively (notably, it's the only Freeplay-only round aside from the generally unreachable round 10001 where no blimps whatsoever are present). Round 263 is very similar to Round 63 in terms on the size of each wave... except Lead Bloons are replaced with (often Fortified) MOABs and the Ceramics are replaced with Fortified DDTs, which can be surprisingly difficult to deal with despite their relatively low health compared to other blimps, thanks to their huge speed and their stacked nature meaning your defense's damage output in this round greatly depends on your towers' pierce (not helped by the fact as, a late Freeplay round, all blimps have 54.5 times as much health as before Round 81).
• Round 90 of BTD6. It's the first round that the D.D.T. appears, and unlike the other intro rounds for the blimps, it doesn't come alone. The round requires that you've specifically prepared a defense capable of bypassing all three of a DDT's immunities alongside enough DPS or crowd-control to pop them before they speed through the map, otherwise they will run you down and end your run in a heartbeat.
• Once you get into the Impoppable rounds of BTD6, the most infamous rounds are 95, 98, and 99. Round 95 gives your abilities time to recharge, starting off with just some camo regrow purples and leads with every possible modifier... then unleashes the biggest D.D.T. rush of the first 100 rounds, with 30 of them and many fortified M.O.A.B.s. Round 98 is a damage race against 30 fortified B.F.B.s and eight Z.O.M.G.s, which is very difficult to overcome on the shorter tracks. Round 99 has fewer D.D.T.s than round 95, but they're fortified and tend to be hard to pop without slowing towers.
• If you've decided to keep on playing a map far past the end of normal rounds, then round 200 is the part where the game decides it's time for you to stop playing. Indeed, the round is made of two fortified BADs, which are twice as strong as regular ones, compounded by the fact that at this point, a BAD has the better part of a million HP. If you previously planned on slowly chipping away at their health using the full length of the track, they will probably be able to leave the map impopped. And if 200 didn't get you, then after it, fortified BADs are permanently added to the random round generator, each one even stronger than the last until you cannot deal with them anymore.
  • And if you manage to survive past that, once you get past Round 250, the game stops pretending to play fair and drastically ramps up the health increase for all blimps, from the hefty but manageable 35% it has been for the previous 100 rounds to a whooping 100% health per round (those Fortified BADs that were getting increasingly more difficult to deal with are now getting 40000 more HP per round, rather than 14000). Similar health per round increases occur on rounds 301(150%), 401(250%), and 501(500%).
  • While it can't be reached without cheating, round 10006 deserves an honorable mention, as from this round onwards the bloon spawns are nothing but 999 Fortified BADs as opposed the random spawning that has been used throughout all of freeplay mode up until this point.

Daily Challenges

The Bloons TD 6 Daily Challenges provide many examples of That One Level on their lonesome—they even offer harder Daily Challenges in the form of Advanced Challenges.

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• Technically, the Co-Op Daily Challenges in BTD6 could indirectly qualify as this. To start off, due to being co-op, the player cannot exit the map without losing all of their progress. If your internet doesn't like you, be ready to get disconnected later in the game, meaning that you must essentially start over from scratch. Alongside, by default the game forces players to group with three other teammates, meaning that the cash gained per pop will decrease heavily when compared with being paired with two players. Unlike normal Daily Challenges, these challenges are capable of having modifiers that are otherwise only seen on Advanced Challenges, so these challenges can disable Monkey Knowledge and predetermine your starting cash. And you better pray to god that your co-op partners are good enough to beat the challenge, since depending on your partner they will be willing to complete the challenge or be mostly doing absolutely nothing or using bad towers and upgrades. However, if everyone else except the player disconnects or leave the game, then the challenge will become easy and treated like a normal Daily Challenge.
  • "Dart Island ~By Simonsok", the Co-Op Challenge for December 20, 2020, really warrants the complaint it gets here by exposing the problems above actively, taking place on Lotus Island with Monkey Knowledge and Powers disabled and having only the following towers allowed: Quincy, Dart Monkey 2-4-5, Buccaneer 5-0-5, Ace 5-0-3, Heli Pilot 5-3-5, Super 0-3-2. To elaborate, the Leads from Round 28 make sure that the players have to realize in a Guide Dang It! moment that they have to allocate funds to either the host to get Quincy to Level 7 for explosive arrows, or whoever will get Razor Rotors for Heli Pilot, with no other options available.^{Other Lead popping} Dart Monkey x-x-5, Ace 5-x-x, and Heli Pilot x-x-4 can damage Leads but cost even more by a wide margin and thus are too far out of price range for Round 28. Not only is this a Guide Dang It!, but if the players aren't cooperative, nobody will be able to afford either option. As if that isn't enough, the challenge lasts to Round 60, resulting in the players having to deal with Round 59's Camo Leads, the obvious solution being to crosspath the Razor Rotors Heli Pilot with the middle path, which some players don't even realize, and one guy who did realize as much reported about the challenge making the allowed group control atrocious.^{Group control explanation} Dart's top path is limited to the second upgrade preventing usage of the Spike-O-Pult and above; Buccaneer can't even use its middle path at all to have Grape Shot; Ace, while capable of flooding the map with darts, isn't cost-effective against clusters when focused on the top path; and Super, with his focus against singleton targets, isn't even worth considering. That would leave the aforementioned Heli Pilot, and Razor Rotors has to choose between the bottom path for faster firing, or the middle path for the Camo Leads. Suffice to say that this has caused plenty of outrage.
• Any challenge that requires extremely fast micro to complete, particularly if you have to quickly sell and place towers instantly or constantly change tower targeting. These challenges will often be lashed for being fully disadvantageous to mobile players, who cannot use hotkeys to make it easier to manage the micro.
• "That's Gotta be the Best Pirate I've Ever Seen", the Advanced Challenge for May 31, 2019, consists solely of beating Logs on CHIMPS from Rounds 15-40... except that you can only use one monkey buccaneer, period. If your buccaneer placement is a few pixels off, a bloon leaks and you die instantly due to CHIMPS making you a One-Hit-Point Wonder. If you fail to micromanage the buccaneer's targeting at very precise moments? Same result. To make things worse, CHIMPS also prevents you from using any powers or insta-monkeys to help the buccaneer out. You also cannot sell the Buccaneer to change its upgrades, and CHIMPS stops all Monkey Knowledge from having any effect.
• "Camo", the Advanced Challenge for June 4, 2019, quickly became notorious due to the Forced Level-Grinding necessary to even stand a chance at beating it. It's either Unwinnable by Design for anyone with insufficient Monkey Knowledge, Powers, or Insta-Monkeys, and it merely becomes excruciating even if you do. Not only does the challenge not provide players enough starting cash to buy any towers without the correct Monkey Knowledge upgrades (which require much grinding to collect), your income is also halved the entire time, due to the challenge being set on Half Cash mode. You have to survive from Round 3 all the way to Round 80 like this, and the MOAB-class bloons in the challenge are given extra health and extra speed. The only towers that can make a dent to any of the blimps are druids (whose damage-per-second can be only maximized by leaking lives; if you do not have anything that regenerates your health, you're out of luck) and MOAB Maulers, the latter of which shoot too slowly to rely on. That's not going into the titular threat, the camos. You must save up for a Signal Flare by 33 to kill the camos there— which is harder than it sounds on Half Cash mode.
• July 6, 2019 was not a good day to do your Daily Challenges, as both the Advanced Challenge and Daily Challenge qualify as this. To make it straight, they are both Unwinnable by Design for anyone with insufficient Monkey Knowledge. The Advanced Challenge "Turon's Challenge" is nigh on impossible to beat without powers or continues, as you have to deal with fast bloons, which also includes high health ceramics and MOABs on Apopalypse mode. The only thing that can pop those ceramics and MOABs is the highly expensive Bloon Crush. Even with maximum Monkey Knowledge, this challenge will burn your Monkey Money and Insta-Monkeys. But worse is the "Oof" Daily Challenge, which is impossible to even complete without enough Monkey Knowledge or powers. You basically start with only Monkey Subs and Buccaneers - on Cracked! The map doesn't start with water, so you must save up to remove the rock and place your towers on the water underneath. If you do not have enough Monkey Knowledge, you will lose all of your lives before you are able to place anything unless you use powers. "Turon's Challenge" was eventually nerfed to be beatable... with only six hours remaining to complete the challenge, meaning that if you lived in a timezone where those six hours were smack dab in the middle of your bedtime or workday, you were still out of luck.
• July 18, 2019 had "Random I". You are supposed to beat rounds 28 to 84 on Half Cash mode (keep in mind that Half Cash mode normally only goes up to 80), with only Pat Fusty, boomerang throwers, and four wizards. If that doesn't sound bad enough, every single bloon that is not a blimp is camo. This includes the ceramics that drop out of the MOABs, mind you! This means that those boomerang throwers cannot do anything 90% of the time until a wizard with the Shimmer upgrade removes camo properties from the bloons. Not to mention that the camo bloon horde includes camo purples, which the wizards cannot damage at all without the Necromancer upgrade, or having Shimmer remove the camo and having the boomerangs or Pat kill the purple layer for them. Unfortunately, the bloons are given increased speed as well, which can cause Shimmer to downright miss some of them and reduces the damage they take from Wall of Fire. Also, the very strict tower restrictions mean that you cannot just plop an insta-monkey and hope that the problems all go away. Even after handling the endless camo rushes, you have the blimps to deal with. And since this is on Half Cash mode, your income is halved the entire time. Fortunately, it was nerfed later on in the day by changing the difficulty level from Hard to Easy.
• The August 28, 2019 AC "RNG is Satan's Greatest Fear" lives up to its name. This challenge is nothing more than a Luck-Based Mission from rounds 10-23 either using only two Wall of Fire Wizards or a combination of an Arcane Mastery wizard and a supporting tier 1 wizard. What's worse is that the bloons are extremely fast and this challenge is on Deflation and CHIMPS. In the end, this challenge has almost no skill aside from placements, and it all just comes down on whether the Wizards will hand you a win or not, which more than likely will be the latter.
• September 2019 began with a rather rude awakening with the September 1, 2019 AC "I To Cray I's Challenge". It is basically a rehash of Turon's Challenge, with it being similarly impossible without using extensive amounts of insta-monkeys and powers due to the bloons being excessively fast (a red bloon will leak in only six seconds - on the relatively long Monkey Meadow of all tracks!) combined with having too much health. Every single flaw of Turon's Challenge is made even worse by the challenge being on Alternate Bloons Rounds, which means that more camos appear early on, and Round 40 hosts a fortified MOAB, meaning that the already excessive bloon health is doubled. You must beat all 80 rounds of Alternate Bloons Rounds to win. You will lose any insta-monkeys you spend on this AC unless you get lucky. It was nerfed very late into the day by reducing the speed increase - but not the bloon health increase!
• The September 6, 2019 AC was changed to a completely different one within a few hours after the rotation time due to qualifying as one of these. Previously called "Eazy", you were supposed to complete End of the Road up to round 80 with only a single Ninja, Super Monkeys and Striker Jones - and the bloons and blimps once again had too much health and speed. Even after a nerf slowed down and reduced the health of the bloons it was still impossible due to players being forced to rely on super monkeys, who have very expensive upgrades. It was nerfed a second time and it was still impossible, leading to the AC being switched out.
• The AC for the very next day (September 7, 2019), named "Camo Madness", was not any better. You had to beat rounds 6-63 with only ninjas, villages, Gwendolin and alchemists. First, all non-blimp layers bloons are camo meaning that Gwendolin cannot hit any of the regular bloons without her abilities unless you get a radar village. In addition, the blimps have maxed health and their child ceramics also have health buffs and move obscenely fast. But this time it's not the bloon speed or health buffs making it impossible - rather, it's the fact that you have to fight off all of this in Half Cash and CHIMPS simultaneously, meaning that you will never have enough money to beat these buffed bloons, and neither can you sell to rearrange your defense nor can you use powers or insta-monkeys to brute-force this. Thankfully it was solved later on after many hours straight of attempts.
• The September 16, 2019 Daily Challenge "Quincey and Rangs" (sic) was a massive jolt to the face in relation to the usual easygoing difficulty of the Daily Challenges in the game. This is due to Quincy being forced to beat Round 51 (consisting entirely of camo ceramics) all by himself due to no other camo detection being available. If you did not get Quincy sufficient EXP to upgrade him to at least level 10, you can kiss your hopes of victory goodbye unless you bought Camo Trap powers, which no Daily Challenge had required before. Even if you bought at least his level 10 ability, Storm of Arrows, you had to time the Storm and Quincy's other ability correctly or else round 51 would still kill you.
• The October 27, 2019 offline AC (only accessible if you disabled your internet connection when you load up the game, since that day had an online-only Co-Op Challenge replace it instead) can be considered the crowning That One Level of all the Daily or Advanced Challenges yet released in the entire series. To make things short, it was Unintentionally Unwinnable. The AC started you off on round 31 on Alternate Bloons Rounds, with powers (and thus also insta-monkeys) disabled. Sounds not so bad? What elevated the AC to infamy was the fact that the starting cash was accidentally set to an unserviceable 300 cash, which could only buy a single unupgraded tack shooter. It was supposed to have several thousand more initial starting cash. To finish nailing in the coffin, the AC was never fixed before it expired, unlike most of the previous Unintentionally Unwinnable Bloons TD 6 advanced challenges.
• The February 26, 2021 AC had to be nerfed seven hours in. You had to finance a Glaive Lord with only an IMF bank to pop the camo green on 24 but you had so little starting cash. Seven hours in, nobody found any permutation of bank gameplay that gave you the glaive lord, and it was nerfed to have more starting cash.
• June 30, 2021's Advanced Challenge made many players very annoyed and upset. The player is forced to use Relentless Glue and Icicles to beat round 59, whose regrow rate has been set high enough to cause quick reduplication of the Regrow Ceramic Bloons at the end of the round. The problem is that the AC seems to run on chaos theory — even reasonably precisely replicated placements of the ice and glue can beat the AC in one attempt but fail in many others, causing a fatally regrown mob.
• August 20, 2021's Advanced Challenge quickly became infamous. The player has to beat rounds 6-24 on Logs CHIMPS with only Striker Jones and Mortar Monkeys. They must accurately micromanage the targeting of both towers, who are neither fast nor very accurate in the first place; this is very bad news as you must fight against fast yellow and pink bloons in addition to explosion-resistant black bloons that contain even more pinks. The official Daily Challenge thread for the day, in addition to YouTube walkthrough comment sections, ended up infested with angry players complaining about the challenge, with the challenge creator attempting to defend himself to no avail.
• May 13, 2022's Advanced Challenge "Go Beyond!!" quickly established itself as the most hated advanced challenge of 2022 - so hated that even its own creator was appalled with Ninja Kiwi's decision to feature it since he had specifically designed it for a friend with a talent for clearing high-micro challenges. You have to remove the camo from a lead bloon and then pop it. The catch? The upgrades are very limited (low tiers only for most towers, and only seven upgrades can be bought maximum) and the lead bloon and its even faster children move at quintuple speed. Pause Scumming and hotkeys are a must, which sadly are not available to mobile players. The only other way to beat it (by using a Flash Bomb) isn't any better, because that route is a Luck-Based Mission instead. The challenge was eventually nerfed by making the bloons only move at quadruple speed instead of quintuple speed, which turned it from nearly impossible to just very tough.
• The aptly named "Hopefully this is fun?" Advanced Challenge was anything but. It consists of completing round 101 of Underground on hard mode. Additionally, the least tiers rule is added, only allowing 10 tiers, among other rules such as reduced speed and health for ceramics and MOA Bs. Because of these rules, in addition to the least tiers rule, the only possible strategy is a 0-2-5 Dart Monkey and a 0-0-1 Super Monkey (set to strong) placed in precise spots on the track. Despite the simple strategy, the challenge ends up becoming heavily RNG-dependent due to the fact that it relies on Crossbow Master's crits occurring enough ^note A crit occurs every 4-8 shots. to clear out the swarm with the Super Monkey only barely helping. What this means is that even if you follow a guide for the placements, you're not guaranteed to win simply because the RNG was not in your favor.
• July 8, 2022's Advanced Challenge "Give A Hug To A BFB" has garnered plenty of frustration, to the point that its creator also was puzzled over its selection. Your task is to defeat Round 78 in Alternate Bloons Rounds (ABR) on Flooded Valley, with only two towers onscreen at once, where regular bloons move 20 times slower, blimps move twice as fast and every regular bloon is a regrow bloon that regrows 15 times faster than normal. So what makes this challenge so quickly infamous? Mostly Guide Dang It! factors this time around:
  • The challenge takes place on Flooded Valley, where most towers cannot reach the bloons due to a giant ledge, making the solution hard to discern.
  • The player is supposed to pop most of the bloons in the round with the explosion generated by MOAB Domination's anti-blimp boomerang. This trick is a Guide Dang It!, as the game never informs you that A) the explosion does anything at all, B) the explosion can affect places where the MOAB Domination cannot throw anything, and C) the explosion affects Zebra Bloons (which are immune to many other explosions).
  • The other problem with the challenge is the extremely tight upgrade rationing. You are capped at buying 45 upgrades and you are expected to use all 45 of them, with little room for error.
• March 27, 2023's Advanced Challenge "Simple Bloon" has been known as little else than utterly rage-inducing. You're supposed to activate a Plasma Monkey Fan Club ability on a very precise frame to beat a fortified lead bloon just before it leaks. Activating the ability requires, at a minimum, obscene amounts of Button Mashing which has an over 99% chance of failure. Many players have torn their hair out as they activate the ability but still leak a yellow or blue bloon.

Odysseys

• While not a hard map on its own, if you ever see High Finance on an Odyssey, you should beware that it will often be the hardest map on the Odyssey it's on. Due to the limited amount of space the map provides and the shorter routes that alternate over time, it comes of no surprise that the map is often placed as the fourth or fifth map and often have modifiers that can greatly spike its difficulty. The map is also not deemed to be extremely hard casually (unlike the aforementioned Geared or X Factor, alongside most Expert maps) to the point where it appears rarely, making the map a common choice for the Advanced map of an Odyssey. The mentioned below weeks 34 and 45 Odysseys are infamous for this, with week 51 "Stun Gun" and 113 "Apes Through Time" also being problematic for this as well.
  • And as usual, seeing Expert maps (that aren't Infernal or Dark Castle) is usually bad news on Odysseys, which also can be greatly impacted by the tower limitations you have and additional modifiers that are included within the map. Even mid-difficulty Experts like Sanctuary and Flooded Valley (the latter of which appears as commonly as Dark Castle and Infernal, which are the easier Experts) can be massively painful when they appear on an Odyssey.
• The Odysseys from the 30th week up to the 36th week started to notably ramp up Odyssey difficulty altogether, resulting in a cluster of various hard Odysseys that are step ups from the previous 29 weeks. However, here are some notable mentions throughout the cluster:
  • Week 30 Odyssey "Stick and Rock Warfare" is the first in the chain, having large amounts of grouped bloons to replace MOABs. The main difficulty comes from the third island on Cracked Half Cash on Hard Mode, where the player has minimal income and tight tower restrictions to pop the grouped bloons. Besides the infamous round 63, the player has to worry about round 60's hyperclumped leads, round 64's hyperclumped camo regrow blues, and round 65's large camo ceramic rush at the very end. Death is very much guaranteed without Wizards and Mortars.
  • The week 33 Odyssey "Bad to the Bone" is considered among the most difficult odysseys to have ever existed, especially in its Hard Mode. The notorious difficulty comes from its last island, taking place on Adora's Temple. You have to beat 85 rounds on Half Cash (note that Half Cash normally goes up to 80, and for good reason!), where your income is halved. That's not the worst part; there are custom rounds. These rounds force you to fight ZOMGs in the 60s (they normally spawn from 80 onwards) and even worse, BADs in the 80s! Remember that you are now supposed to fight rushes of extremely powerful blimps, over 15 rounds early, and with all income being halved and you will be in for a very tough time.
  • While week 34's Odyssey "Rebuilding the Economy" isn't very hard with full Monkey Knowledge (aside from the End of the Road Half Cash on the second island which can be formidable with the tight upgrade restrictions), the first island is rather infamous without any Monkey Knowledge. You only have 14000 starting cash to beat Hard Deflation on Lotus Island with 20% faster bloons, no less. Due to being on Hard, the tower and upgrade costs are increased to the point where it's the equivalent of having a mere 11000 starting cash on Easy. Plus, the tight tower restrictions means you're only limited to tier 3 towers outside of the unaffordable Elite Sniper, Pirate Lord, and Spirit of the Forest. Even with Monkey Knowledge, this island can still prove a challenge.
  • Week 35's Odyssey "Mc Double" ramps back up to "Bad to the Bone" difficulty. Not only all maps are on Half Cash again (this time with some on Hard difficulty unlike "Bad to the Bone"), but the rounds are doubled and all doubled bloons are stacked atop of each other. Most maps also start on round 4 too, meaning you'll have a large swarm of blues you have to pop. Perhaps the most infamous part is when you reach the last island (Rake Medium Half Cash), all bloons in the early rounds isn't just doubled, but rather quadrupled! Have fun without Monkey Knowledge.
• After multiple weeks of easy Odysseys, the difficulty would greatly go back to being hard with week 45's Odyssey "Let's Take to the Sky!". It looks like a typical Extreme Odyssey, but there are custom rounds where all bloon rushes have 0 spacing. Many trivial rounds like round 34, 45, and 54 becomes extremely dangerous thanks to the custom rounds, with so many hyperstacked bloons to deal with. Not helping matters is the upgrade restrictions, which only allows you to use full upgrades on the Heli-Pilot and Monkey Ace, which is rather lacking in pierce upgrades. Every other tower is up to tier 2, killing their viability against bloon rushes. The difficulty selections are rather tough too, and the last map is especially extremely hard to deal with. You are pitted to beat High Finance rounds 41-95 with hyperstacked bloons – on Impoppable with only 12000 starting cash. This is more than 25% less starting cash than the income from beating rounds 1-40 normally. You better hope you have a lot of powers or skill if you want to get past the last map without Monkey Knowledge.
• The Week 50 Odyssey "Mirage" has gained infamy not for being one of the hardest, but rather one of the most tedious Odysseys made. It pits you against Hard Half Cash on all maps, but with custom rounds where bloon sends are doubled by sending the round again after the round is first sent. Many of the maps goes up to round 80 too, meaning you're in for some long waits just to beat a round for this Odyssey. The last two maps, Bazaar and Mesa, can also prove quite a challenge.
• The Week 71 Odyssey "Mageical Journey" brings the return of user-made Odysseys since week 52, and the large difficulty spike between the Ninja Kiwi-generated Odysseys previously showcased at the time can be easily seen. Despite its name (which in reality is a reference to the Three Mage-Sisters), you aren't granted any Magic Monkeys besides a top-path Druid, an Alchemist (without middle path), and a Shimmer Wizard. Instead, you're given an extremely limited set of towers (only one of eight towers, with only a singular Ice, Mortar, and top-path Druid being your main source of popping power) and Monkey Knowledge disabled to clear all the maps, where you have no method of restoring lost lives, many of the maps being somewhat poor for the towers available, and the available towers having extremely lackluster MOAB damage.
• Week 101's "Ruins" Odyssey is perhaps the most hardest and notorious of the Odysseys that can make most of the previous Odysseys look like a piece of cake. Instead of having a consistent rule or theme that most previous Odysseys had, all maps have random and confusing rules that are extremely hard to plan out, all on an Extreme Odyssey and without a theme or ruleset to distinguish the Odyssey. These erratic rules include extremely tough ceramics that are hard to break past round 81 as early as the first map on Lotus Island, 300% fast bloons on Chutes, and an Impoppable on Sanctuary with a cash limitation and no Monkey Knowledge to boot. Since all maps have a tier or cash limitation, you cannot place anything else if you exceed these limits and must restart if your defense fails to hold out. It became hard enough to even break most walkthroughs, many of which relies on using powers to get past the final map.
  • The result of this Odyssey had led to a good amount of later Odysseys to follow its footstep of having no consistent theme in favor of random hard-to-plan rules, with extremely less than satisfying reactions from the subreddit community.
• Week 110's "Revenge, Support" shows how much having only Support only towers can be difficult as a game mode itself. It relies on a small group of Support category towers (of which only the Spike Factory and Engineer Monkey can deal damage), in which you have to face a multiple set of rules that greatly hamper the potential of your defense. Not to mention, many maps also disable Monkey Knowledge or have CHIMPS rules, greatly limiting what you should pick in the first place.
• Week 134's "The Year of the Rabbit" returns with chaotic custom rounds where everything from a ceramic or above is a BFB, and everything below is a red or yellow, making the rounds generally a cash starve. Although it looks dangerous, surviving the 40s will guarantee victory, although such feat will be hard due to the limited amount of starting cash. However, when you do reach the second map, it takes place on Double HP MOABs, so all the BFBs are extremely hard to take down without relying on a full-on budget defense to beat the early game. Have fun without Monkey Knowledge.
• Mini-Luck has one very infamous second island, where you have to beat Karts n' Darts with every single bloon turned into a camo regrow bloon that regrows 7 times faster. Druids with Heart of Oak under a Radar Scanner village are required or else the camo regrow bloons are guaranteed to replicate uncontrollably. Some people who tossed their villages or druids overboard are forced to repeat the first island to have a chance here. Even with the druids, poor tornado luck can cause regrow madness anyhow.

Bosses

• You're usually in for a rough time (especially on Elite) if you see a boss on an Intermediate map or especially an Advanced map. Due to the shorter paths that isn't adjusted for the bosses, you have way less time to dish out damage to the boss before they leak, which is especially bad if the boss happens to be Lych or Vortex, who are faster than the other bosses.
  • It's even worse if it happens to be Vortex on a multipath map. Due to how Vortex's bloon speed mechanic works, only the bloons on the path Vortex is on is limited by how fast they can go based on where Vortex is^note Bloons that are behind Vortex will go faster only if it is on the path it's on, otherwise they get a permanent speed boost as long Vortex is on screen., while the other path(s) are permanently faster as long Vortex is still on the screen. Having the hassle to deal with the faster lane of bloons and Vortex at once leads to a painful experience in the end, especially against Elite Vortex.
  • As of now there has been only one boss event on an Expert map, and that was week 77. It was on Dark castle which is generally considered the easiest of the Expert maps, and the boss (Vortex) had a speed reduction to 70% speed.
• A Lych event that took place on The Cabin was at the time one of the hardest Elite boss events done. With Benjamin disabled and taking place on Hard with a poorly-shaped map for farming, affording paragons necessary to defeat Elite Lych was a difficult feat to accomplish. Almost no Elite bosses have taken place on Hard as a result ever since.
• A nasty surprise arrived when the Lych event on Scrapyard took place shortly after the release of Vortex. Due to a bug, Lych Souls gained the ability to ramp via Freeplay rules. This affected its speed and health, so a tier 5 Elite Lych Soul had well over 1,200,000 health with a speed as close to a DDT^note For reference, a non-bugged Lych Soul normally has up to around 500,000 health and has a speed in between a BFB and a MOAB.. Immediately after the bugged event was released, the remaining Lych events for that update took place on Easy on Beginner maps to counteract the bugged Lych Soul.
• Vortex on Quiet Street and Chutes. Awful map combinations where most towers are easily going to be stunned due to the massive stun range Vortex has while towers are grouped up due to the poor map shape, alongside having numerous support towers disabled (both disable Dart Paragon to make it harder to deal with Elite tier 3, and the latter also limits how many farms and total towers you can have, weakening your farming and Paragon potential). Have fun beating Elite.
• Lych on Haunted. Not only is the map short for the rather fast Lych, but Monkey Knowledge is also fully disabled, making it more difficult to farm for sufficient upgrades or use Mana Shield to tank some of the lives Lych Souls can steal. This difficulty was so much that there was not even a ranked time for Elite within the first 24 hours of the event.
• Week 87 put Vortex on Monkey Meadow, with a bloon/MOAB speed modifier stacked on top of a Boss speed modifier. The map choice is deceptively difficult, since the tight overlapping paths and emphasis on clustering mean Vortex can stun defenses very easily, and its massively boosted speed means it can traverse the long track and close the distance to your defenses alarmingly quickly. The standard bloons are no slouch either, as the massive speed boosts combined with Vortex's slipstream can turn them into supersonic menaces, especially Ceramics/Super Ceramics since the event also buffs Ceramic HP. On top of that, it's on Hard difficulty which hikes up tower prices and makes farming more difficult, although you do get a lot more starting cash. Even after all of this, it's somehow easier than the original version on the event's release, where Vortex lacked the Boss speed modifier but had stacking MOAB/Boss HP modifers, making it an incredible damage sponge for its speed. ^note It's worth noting that the changes to the event were not directly because of the difficulty, but in order to fix a bug where Vortex would take massive damage from loading quicksaves.
• In late October 2023, Vortex would be put on In The Loop. While it seemed fairly easy at first, with a large cash start (1600) and allowing all Paragons to be used at once, the elite version would prove to be very difficult, with 190% Boss speed. Tier 5 would prove to be a very tough challenge even with all 7 Paragons on the track.

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