Demonic Spiders / Terraria

These monsters can make even the most battle-hardened Terrarian cringe in terror.

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Caverns/Underground

• Literal spiders, three of which are perfect candidates for this trope. The Blood Crawler is detailed more in the 'Crimson' section below, but as for the underground spiders:
  • Wall Creepers, found in their own Spider Cave mini-biomes in the Cavern layers underground. If you thought Blood Crawlers in the Crimson had high spawn rates, just wait until you dig your way into a Spider Cave and find a horde of these creepy crawlies skittering straight towards you. Attempting to fight them early on with conventional melee weapons is pretty much suicide, as they are even more resistant to knockback than their Crimson counterparts while dishing out just as much damage, and with the mini-biome you encounter them in covered in sticky cobwebs, they're likely to knock you into a patch, dogpile and make mincemeat of you in a few seconds if you're not careful.
  • In Hardmode, these Wall Creepers get replaced by the even worse Black Recluses, which deal very huge damage, have even higher spawn rates AND inflict Venom, which drains your health much faster than Poison. Expert Mode makes the Black Recluse even more dangerous by giving it a web spit attack that immobilizes you completely for a second or two; given the Black Recluse's high damage and tendency to attack in swarms, this will most likely kill you.
• Hoplites from the marble biomes can throw large javelins which deal massive amounts of damage and strike with surprisingly deadly accuracy, letting them snipe you in a few hits if you can't avoid their line of sight or continuously pile damage onto them. Considering that the marble biome is relatively common, it's painfully easy to encounter them unprepared while mining, and they can easily two-shot a player without enough health upgrades.
• Medusas in the marble biomes. If they catch you in their line of sight, they can use an attack that will turn you to stone, which paralyzes you for around 1-4 seconds based on how long you were caught in the attack. But that's only the start. Medusa can potentially chain this attack and keep you paralyzed for much longer, while other enemies have free reign. Furthermore, being paralyzed negates almost all forms of fall damage prevention and amplifies fall damage, so if she or anything else knocks you off a ledge, it's likely going to be fatal. The only upside is that you have to be facing her and have a clear line of sight for the attack to work, so killing her is pretty easy if you have some spare blocks and a yo-yo. The 1.3.1 update fixed some of these issues by limiting them to Hardmode-only monsters, removing all early-game threat from them, and making it so they can't petrify players directly above them or petrify players while off screen (which would cause you to get petrified without ever seeing the medusa, often while not on the ground). Update 1.3.3 would further nerf them by introducing an accessory they can drop called the Pocket Mirror, which grants immunity to petrification and is now baked into the crafting recipe for the Ankh Shield, so killing enough of them can completely nullify their most annoying attack.
• The Nymphs. Unprepared players will only see a harmless Lost Girl, assuming she's an NPC of some sort. But when you get close, they flip out and chase after you, dealing massive melee damage. Sound familiar? Of course, after falling for it the first time, the player can shoot the Nymph from a distance for easy damage. Their saving grace is that they are extremely rare, which in turn can become annoying if you're trying to find a Metal Detector.
• Armored Skeletons in Hardmode, which can inflict the Broken Armor debuff, which used to half your armor rating for five minutes turning even the weakest of Hardmode enemies into a serious threat. Later patches nerfed this down to only a couple minutes at most, but considering they can be encountered in almost any underground environment, you'll likely have to deal with a lot of these guys and can easily get overwhelmed.
• Giant Bats, and their tougher Hallowed cousins, the Illuminant Bats. They're everything bad about bats - fast, comes in huge swarms, hard to see, harder to hit - with insanely high attack power (especially in the case of the Illuminant Bat, whose attacks consistently deal 40+ damage even with the game's best armor) and, in the former's case, a small chance of inflicting Confusion, which reverses your controls and has led to many a death from accidentally walking into lava.
• Rune Wizards. The hardmode, much less whimsical version of Tims, they shoot powerful projectiles that can pass through solid blocks and cannot be deflected. They are also deceptively tanky, being almost twice as hardy as most of their armored cousins in the hardmode dungeon despite looking and acting like a typical Squishy Wizard. Most players would reasonably attempt to close the distance and kill them with a sword like with most of the wizards they've encountered, but for some inexplicable reason, they deal more contact damage than any other regular enemy in the entire game, doing 200 damage (400 in Expert mode, and a ridiculous “600” in Master mode!) which makes their Tele-Frag a lot more powerful than it should be and makes it dangerous to even try and use melee without bumping into them and losing over half your health (or in Master, all of it). To put that in perspective, the spells they cast are only 90 damage (180 in expert), less than half, and the Crawltipedes, the strongest enemies of the final event of the game, the Lunar Events, only deal 150/300 head-on. The only attacks that meet this damage are the Clown's bombs, which do the same, the Martian Saucer's desperation deathray, which deals 100 more, and the Dungeon Guardian, which just flat-out kills you.

Snow/Underground Snow

• Spiked Ice Slimes lack the range of their tropical cousins, but they have crazy high rates of fire and can inflict the Chilled and Frozen debuffs.
• Pigrons turn invisible and fly through walls. While their damage is fairly negligible, they're nearly impossible to see until they hit you.
• Wolves are the Snow Biome's answer to Unicorns. Thankfully only appearing at night on hardmode, they can charge from nearly out of nowhere, track you, and soak up a lot of damage for an early hardmode player's weapons.
• Ice Elementals and Icy Mermen are rather irritating. Both fire bolts of frost at you from a distance whenever they have line of sight, which can inflict Chilled to slow your movement. The former floats around and hits harder, which makes creating separation more difficult, while the latter fires more quickly and also has a chance to freeze you in place for a few more free hits.
• Ice Golems, found during Hardmode blizzards. They have a large amount of health (especially on Expert, where they have almost as much health as the Wall of Flesh, are almost completely immune to knockback, and fire highly damaging blue lasers that Chill players for an extremely long duration (up to 1.5 minutes on Expert). The worst part about them, however, said lasers also have a 20% chance of freezing you solid and rendering you helpless for a good 1-2 seconds - giving it or other enemies a chance to hammer away at you.

Desert/Underground Desert

• Pre-Hardmode, a starting character should take caution when traversing the Desert surface as there's a chance that Antlion Swarmers can spawn, or rise out from the pit to the Underground Desert. These are flying enemies with a good bit of health at that point, move extremely fast, and hit very hard. They will also relentlessly chase down the player without much problems thanks to their sheer speed and knockback resistance. And if there's a sandstorm going on, they won't even require desert background walls to spawn.
• Desert Spirits in the corrupted/crimson underground desert. They teleport around like Dark Casters, except instead of just shooting projectiles at you, they summon little projectiles near you that home in on you, pass through blocks, and EXPLODE. So not only do you have to chase them down, half the time you don't even know where they're attacking from - and it doesn't help that you meet them in the underground desert, which is riddled with holes and pockets that the pesky things can and will use to blast you to bits in safety, given they'll likely teleport away by the time you've noticed them and dug to their location. To make matters worse, if you don't kill them after they attack once, they will cast that attack 5 times in succession They can easily shred unprepared players without even showing themselves.
• Tomb Crawlers and their hard mode equivalent Dune Splicers. For a worm, these things deal really high damage, and are thicker than most worms (Dune Splicers are even as thick as the Eater of Worlds.), meaning you are more likely to get hit by them. Additionally, the narrow passages of the underground desert mean that you'll generally not see these things coming until you've already been hit. To make things even worse, the Dune Splicer's gigantic hitbox combined with the cramped space underground mean that it can easily trap you in a spot where it then hits you multiple times in succession, with nothing you can do about it. And if you thought that was bad, in Hardmode they spawn en masse during sandstorms - as in, if you kill one, another one will almost assuredly take its place instantly.
• Sand Sharks. In case you needed even more affirmation that you should stay out of the desert during a Hardmode sandstorm, these things also spawn amongst Dune Splicers in droves. They hit very hard, have a lot of health, and are extremely irritating to damage due to their swimming in the sand causing most attacks to hit the sand instead. Worse still, if you happen to be in a desert overrun by the Corruption/Crimson/Hallow, these things have biome-specific cousins that do even more damage and are even more resilient.
• Basilisks are pretty much Antlion Chargers on steroids. They deal high damage, have an insanely fast charge attack, and can soak up a decent amount of damage. They can also show up in underground tunnels where you have literally no room to dodge their charges; if you get backed into a corner by one of these guys, you're dead meat.

Jungle/Underground Jungle

• In the underground jungle, you have Hornets, which range from tiny but dangerous to large and absolutely deadly. Even the weakest version does a fair amount of damage, they inflict the Poison debuff for at least five seconds, and the jungle spawns them in packs. They also preserve their momentum when they hit a wall, meaning they can pinball around at very high speeds making them very hard to hit with magic or projectile weapons all while firing stingers at you. The accepted strategy for dealing with them is to wall yourself up and hit them with either a wall-piercing weapon or a yo-yo, which can be squeezed through a one-block gap. In Master Mode, the damage the Hornets themselves do pales in comparison to the poison they inflict, which can last as long as thirty seconds for one hit.
  • The console version introduces Dragon Hornets, which are stronger than normal Hornets. Insultingly, they don't even have good drops, leaving only a pittance of copper coins.
• Man Eaters, meanwhile, are basically a pair of mandibles on the end of a stick, and they can reach through walls to chomp you, leaving you helpless - and the Vilethorn does fuck all to hurt them. They're tougher versions of the Snatchers you find on the surface that stretch twice as far, and you'll find that these types of enemies are much more suited to attacking underground because you can't see them coming from within the mud blocks until they chomp you for 30+ damage. Their hardmode equivalent, the Angry Trapper, is even more troublesome in this regard - if you can see it on the screen, nine times out of ten it can reach you and chomp at you for an obscene amount of damage.
• Spiked Jungle Slimes have incredible accuracy, powerful attacks that can poison for much longer than hornets, and are harder to see than Hornets.
• Arapaimas in the Hardmode Underground Jungle. No real tricks about them - they're just big fish that are faster than you and really, really powerful. If you fall in the water and get swarmed, you're not getting out.
• Moss Hornets in Hardmode take everything bad about regular Hornets and make it worse. They fire their stingers like machine guns, hit rather hard if you don't have at least Hallowed armor, can travel through water, and can poison you. They generally have impeccable aim as well, so get used to jumping around a lot to throw them off. Melee oriented players without a decent ranged weapon will also have difficulty with them due to their tendency to fly away from you if you try to get close to them. They also like to attack you in groups and are extremely common.
• Giant Tortoises have an insanely powerful spinning pile-driver attack that can strike seemingly out of nowhere and easly deal half of your max HP on hit. They are the reason why players new to hardmode should stay out of the Jungle. Ice Tortoises in the Underground snow biome also do this, but they do less damage and at least give off light, making them easier to see.

Ocean

• Sharks are fast, take off huge chunks of health with every bite, and can take some serious punishment. However, they're only found in the oceans, so you pretty much have to be trying to encounter them.

Sky

• Wyverns. These giant flying dragons occasionally spawn around floating islands, just slow enough that you might be tempted to drop your guard before they appear from above headed straight for your head. Making sky homes is out of the question with these guys around. They hit insanely hard for early hardmode, have lots of health, and have much greater maneuverability than is common for a worm-type enemy. You also can't outrun them once they've spotted you; they'll chase you even if you teleport to your spawn. And you have to fight these things to get wings in the early hardmode. The bastards also have a tendency to spawn while you’re building things in the sky or even when fighting bosses, making such activities even more treacherous. The console version one-ups them with the Arch Wyverns.

Corruption/Underground Corruption

• Eaters of Souls are the basic Corruption enemy, generally being more like Goddamned Bats than this trope. However, they can easily be this trope to new players, as the geography of The Corruption causes them to spawn in large groups, and all you need to do to encounter The Corruption is to explore the surface - a surface that is littered with large chasms that they can and will spawn from, and will gleefully shove fresh players down to their deaths, assuming they haven't acquired mobility upgrades such as grappling hooks and double jumps by this point.
• Corruptors are tougher versions of the Eater of Souls with a nasty ranged attack. Before the 1.2 update, said ranged attack also corrupted terrain wherever it hit, helping the Corruption's already fast spread rate. They also have a small chance of inflicting the irritating Weakened debuff whenever they hit you. Finally, like the Eater of Souls, they often swarm the Corruption in large numbers.
• Clingers, tougher versions of the Man Eaters that spawn in the underground Hardmode Corruption. They shoot cursed flames that don't go out when you jump in water, can move through walls, and tend to be grouped near each other. Made even worse if a Corruption spot has spawned under your house.

Crimson/Underground Crimson

• Blood Crawlers are giant spiders, with stats akin to and slightly weaker than Wall Creepers, but what makes them particularly dangerous is that, unlike Wall Creepers which spawn specifically in Spider Cave mini-biomes underground, these things spawn on the surface in the Crimson biome constantly, have high health and hit hard for being an early-game enemy. They can easily catch up to fresh players without good armor and movement upgrades and rip them to shreds within seconds. Worse still, they spawn much more frequently and clamor around on the walls to get you while you're traversing a Crimson chasm, making summoning the Brain of Cthulhu an even more arduous task for early-game adventurers.
• Face Monsters. Not much to say about them other than the fact they are faster and very resilient versions of zombies. At the point you encounter them, you probably don't have any guns or good melee weapons, so you can't push them back or delay them.
• Ichor Stickers, for similar reasons to the Armored Skeleton listed above. Their Ichor debuff also reduces your defenses, in this case by 20 points. The good news is it only lasts 15 seconds, not a couple minutes. The bad news is that unlike Armored Skeletons, which have to physically touch you to apply their debuff, Ichor Stickers can apply theirs from extremely long range with their high-velocity spit. And they can also fly, making it harder to retreat from them.

Hallow/Underground Hallow

• Unicorns. They're heavy hitters that dart towards you at high speeds as soon as they spawn in, and they shrug off attacks and knockback like it's nothing. Light Is Not Good, indeed.
• Gastropods, which only appear in the Hallow during the night. Thank god for that—their lasers are one of the few ranged attacks in the game which is neither deflectable nor easy to dodge, and they hurt, even with good armor. Adding insult to injury, their small size means it's basically impossible to beat one in a Sniper Duel unless you have really good aim and/or homing projectiles. If you get swarmed by a lot of them, you better pray you have your Deadly Dodging skills up to the hilt.
• Chaos Elementals are incredibly fast and can teleport at will, including directly on top of you. They used to be especially irritating because their tendency to Teleport Spam meant the only reliable way to deal with them was to swing a melee weapon wildly and hope they materialize in front of you enough times. This has been toned down, and now Chaos Elementals will only teleport to you if they are stuck or cannot reach you, but this still means nowhere is safe to hide from them.

Dungeon

Note: The Dungeon only enters Hardmode after Plantera has been defeated.

• Necromancers in the Dungeon that appear during Hardmode. As soon as they take damage, they teleport and shoot highly damaging beams. The catch? The beams bounce off walls and are incredibly fast, making it incredibly hard to dodge and avoid being damaged. As if that's not enough, the beams have a chance of inflict a slowing debuff.
• Their counterparts, Diabolists and Ragged Casters, aren't much easier to handle. Diabolists also teleport like crazy, but they shoot explosive magical projectiles with huge area of effect explosions that linger for a while. Ragged Casters fire rapid-fire magical projectiles that inflict the Blackout debuff, which is like Darkness but worse. They are the only Hardmode dungeon caster enemies that don't teleport away upon being hit, which was probably an intentional balance measure, since their projectiles chase players for huge distances, ignore walls, can't be destroyed, and deal stupid amounts of damage. Poems have been written about how frustrating Ragged Casters are to face. As the final insult, the Spectre Staff, dropped by Ragged Casters, doesn't even have the same wall-clipping, rapid fire properties as the Casters themselves.
• In Hardmode, Skeleton Snipers can deal out tremendous damage from incredibly long range, often shaving off more than half your HP in a single shot (if not outright one-shotting you). Even worse, they tend to blend in with the mobs of other skeletons. If you're below half health, you best be watching for these menaces, lest you want a high-velocity bullet out of nowhere to send you packing.
• Paladins essentially force players to target them once they appear, because they have a titanic amount of health and will rapidly fling highly damaging hammers at the player if not kept in hitstun. If a Paladin appears together with a caster-type enemy, retreat is often the only option.
• In Hardmode, Skeleton Commandos can pose a serious threat. They blend in well with the other skeletons in the dungeons and their rockets are fast, long-ranged and pack quite a punch. In addition, because of their blast radius, even an indirect hit can be deadly.

Mushroom

• The reason why one shouldn't spawn a surface Mushroom Biome before Hardmode (unless they're well equipped) is because the mooks there have loads of health and deal very high damage; even the zombies in Mushroom Biomes have roughly three times the damage and 4-5 times the health of their regular counterparts. Special mention goes to the Mushi Ladybug, which hurts much more than the other foes there, moves very fast, has very high knockback resistance, and can fly for short distances.
• The Giant Fungi Bulb is a constant threat in hardmode Mushroom Biomes. It behaves similarly to the Man-Eater, only it will also shoot spores that float erratically, deal a lot of damage, and can pass through solid objects. Because of these menaces, it's a good idea to bring something like the Death Sickle or Nettle Burst if you're wanting to explore Mushroom Biomes.

Underworld

• Bone Serpents found in the Underworld. You are surrounded by lots of lava (which kills you very fast), and they have lots of health.
• Demons in general are a huge nuisance to deal with. These denizens of the underworld fly around quickly, can take a beating compared to all the other Pre-Hardmode enemies you've fought before, and toss deadly sickle projectiles that not only hurt like hell but also inflict you with the Darkness debuff which dims your vision for a short amount of time, making it more difficult to see other enemies and more sickle projectiles heading towards you, which can extend the debuff even longer.
  • There are also Voodoo Demons, which are basically Demons with slightly boosted HP and the Guide Voodoo Doll as a drop. What makes them especially dangerous is that if you aren't careful when you kill them, they might drop the doll into lava when they die, which summons the Disk-One Final Boss, the Wall of Flesh, who is no pushover, especially if the player is under-prepared or doesn't have good movement options. It's not that they're particularly dangerous on their own, it's that you deliberately have to engage them over solid ground to avoid accidentally summoning the Wall of Flesh, since it doesn't distinguish between intentional sacrifices and accidental sacrifices. Also, since the dolls don't stack, they'll fill up your inventory pretty quick if you're trying to carve out a path for the Wall of Flesh.
  • Later on in Hardmode, once you defeat a mechanical boss, a new type of demon called the Red Devil appears. They can fire 5-6 dark tridents that each deal massive damage ^note (120-150+ even with Hallowed Armor)! Thankfully, they're rare and their tridents are slower than Demon Scythes.

Events/Other

• The console version introduced a lot of these, with many of them being reskins of previous enemies with boosted stats. Examples include Dragon Hornets, Arch Demons, Orcas, and Arch Wyverns.
• Clowns only appear on hardmode Blood Moons, and very rarely, but they are this game's answer to Creepers, throwing bombs that can destroy terrain. Thankfully, 1.2 changed it so that their bombs no longer destroy blocks. The bombs still hurt like hell though.
• 1.4 added five new menaces to make fishing during Blood Moons nerve-wracking, because you just might fish up one of them instead, and three easily make this list.
  • The Blood Eel is about as annoying as any other Wyvern, and doesn't even have the decency to drop any Souls of Flight.
  • The Dreadnautilus is a full-on miniboss, with the ability to summon flying squids, fire blood spikes from its beak, and rocket around at top-speed deflecting projectiles with its shell.
  • The Hemogoblin Shark. Practically a living Jump Scare as it immediately takes off at top speed when fished up, swimming across any bodies of water in moments, able to run about as fast, jump long distances, and vomit blood in a massive spray if none of those can reach you.
• Goblin Sorcerers don't pose much threat to a prepared player, but before the 1.3. update that allowed NPCs to fight back, they are excellent at killing your friendly NPCs by either teleporting into their rooms or hitting them with their projectiles. But at least the Vilethorn can dispose of them quickly.
• The Solar Eclipse has a few particularly infuriating enemies:
  • Mothron. Sure, it's rare, but this miniboss-level enemy hits hard, and is the sole Solar Eclipse enemy that can fly through blocks in a manner like Queen Bee (instead of "floating" through them like the Wraith/Reaper), meaning that it's no longer safe to barricade yourself in, even in a wraith/reaper-proof house.
  • Vampires are this if you don't have a Stake Launcher to deal with them, as they're very durable and tend to fly in unannounced at high speeds and bite you, dealing heavy damage and preventing your life regen from working for a brief moment, which makes all the difference when fighting other enemies such as Mothron or Eyezor. While in their flying bat form, they also have a small hitbox, making it hard to hit them with a non-homing weapon.
  • Butchers. They have a durable amount of health, charge at you with extreme speed, and their chainsaw deals heavy damage and can hit you through walls.
  • Eyezors are significantly tankier than the other enemies in the event and rapidly fire long-ranged lasers with pinpoint accuracy, letting them tear off chunks of HP before you can even see them coming. To make matters worse, they blend in remarkably well with the rest of the enemies, and attacking them does little to stop their lasers.
  • Nailheads fire rapid spreads of nails which deal very high damage on higher difficulties and can be difficult to avoid while you're dealing with other threats, along with massive contact damage to make melee fighting them risky. Worst of all, however, they pack a titanic HP score that rivals some bosses, ranging from 4,000 to 12,000 depending on difficulty; this makes them extremely hard to kill, especially if they're in a group of mobs that are already soaking up your fire.
• The Solar Pillar is generally agreed to be the worst of the four Lunar Event pillars, and for good reason.
  • As long as you're in its area, it will summon the Crawltipede, a massive, flying worm that deals huge Collision Damage and, like Moldorm, can only be damaged by hitting the small glowing ball on its tail (though, on the plus side, it takes 10 times your base damage with each hit). Thankfully, they only attack airborne players, but this thing considers airborne to be about eight blocks above the ground, and will chase you down like a homing missile on crack until you're on solid ground again. Even if you kill it, it just comes right back. This makes fighting the very fast, melee-based enemies that much more obnoxious, since it foils the Cosmic Car Key and even basic wings.
  • The solar biome in general is pretty rough for anyone. In addition to "no going airborne", there are monsters who can reflect your projectiles back at you (Selenians), and there are no major visual clues as to them having done so until you take the hit. Each pillar tries to make its respective type (ranged/guns, magic, melee, summon) the easiest style to use against it, but the Solar Pillar is the only one that outright punishes you for trying anything other than its respective strategy (melee). Thankfully, a way to cheese both the Crawltipedes, Selenians and almost everything else is to hide in a box of solid blocks and using a penetrating weapon, but this doesn't stop the Corites from tackling you if you don't kill them in time.
  • While the Vortex and Stardust pillars can summon enemies to deal damage, the Solar Pillar is the only pillar which can attack the player directly by spitting fireballs.
• Of the remaining three pillars, the title of most annoying has to go to the Nebula Pillar, mostly due to these two enemies.
  • The Nebula Floater found here uses a highly damaging laser that is rather hard to dodge due to blending in with the background and moving extremely fast. It also teleports whenever attacked, which makes fighting it without getting hit at least once difficult.
  • There's also the Evolution Beast, which has a good bit of health, and fires a purple Painfully Slow Projectile. Said projectile homes in on you, pursues for a good bit of time, hurts a lot and will keep damaging you as long as you're in contact with it, and passes through terrain, forcing you to keep moving around and possibly into the path of Brain Sucklers. And if you've already got a Brain Suckler on your head, it's nigh-impossible to see the purple balls coming.
  • ...And that's on top of the nightmares known as Brain Sucklers harassing you. The Sucklers come in droves, move extremely fast and latch on to you for a constant stream of damage, in addition to inflicting you with a souped-up form of Blindness called Obstructed that reduces your vision to a tiny circle around your character. Chances are that the Sucklers will either shred your health or allow other monsters to do it for them.
• Just because the Solar and Nebula Pillars are the hardest doesn't mean that the other two are much easier.
  • The Flow Invaders spawned by the relatively-tame Stardust Pillar. They have a lot of HP and rapidly fire rocket-like projectiles that are hard to dodge and hit very hard. While it has limited ammo, its minions regenerate at such a fast rate that it can keep up a constant barrage most of the time. And if killed, they will launch all their remaining minions in a devastating spread that is extremely dangerous. Thankfully, it's possible to avoid them by hiding behind terrain, as these minions can't pass though terrain.
  • Alien Larvae in the Vortex Pillar's area are nearly harmless. They then evolve into Alien Hornets, which can dive-bomb you but are still rather easy. But the Hornets then evolve into Alien Queens, horrendously powerful enemies that can hover a safe distance from you while firing energy bolts like machine guns. The bolts do massive damage and inflict Distorted, which causes your character to bob up and down in midair uncontrollably, making you easy targets for the Queens. And to top it all off, they spawn several Alien Larvae when killed, which can then evolve into more Queens if not killed fast enough.
  • Storm Divers encountered in the Vortex Pillar are arguably the biggest threat of everything there. They can hover and glide around, are quick on their feet, tend to show up unannounced during the chaos, can appear in packs of three or four at a time, and fire shotgun blasts that chunk you for nearly half your health even with some of the best armor in the game. Paired with Alien Queens, which can lock you at certain altitudes with their Distortion debuff, and you'll often get blasted to pieces before you get another chance to heal up.
• Dart and boulder traps, while not "monsters" in the usual sense, are very dangerous for a low-level player. The triggers for both are hard to spot unless you're actively looking, which you won't be doing because there's about five other things to pay attention to. Dart traps blend into stone blocks, so you likely won't spot them either. The darts they fire move extremely fast and do a lot of damage, to the point that they'll probably hit you before you know they've fired and will outright kill players without life upgrades. It's telling that the game has an achievement for dying to one, so it knows they're likely to bring you down. And since dart traps are blocks, you can only mine them up, not destroy them like monsters. Boulder traps aren't quite as bad, but they do a lot more damage and used to be able to kill even players with max health and good armor due to having an armor-piercing property. If you trigger it, it will fall right on top of you and will probably hit you.
  • 1.4 adds Rolling Cacti to the Underground Desert, which are a double-edged sword. Upon being hit with any source of player damage, they will start rolling like a Boulder before exploding into a thorny explosion on impact. The bad side is that these things can be unexpectedly set off by a player attack, upon which it may promptly bowl them over for an obscene amount of damage (reaching 300+ on Master). The good side is that players can also send them rolling to run over enemies for massive damage.
  • Explosive Traps used to be this. If triggered, they explode in a 10-block radius and inflict 500 damage to all entities, which will one-shot any pre-hardmode player. They used to be wired to nearly invisible pressure plates, until an update changed that to very visible plunger detonators. However, the old pressure plate version still spawns underground, making it very dangerous to jump into a cave you haven't explored yet.
  • Furthermore, 1.4 also introduced Dead Man's Chests. These chests are hidden underground, looking like normal Gold Chests at first glance. However, they are surrounded by a multitude of traps around them, usually a combination of Boulders, Dart Traps and Explosives. These traps have the potential to one-shot a character in endgame gear, but thankfully, they can be disarmed by simply mining the Explosives and Dart Traps and blocking the Boulders with solid blocks. However, these chests can only spawn as Gold Chests, making any other variant of chest found underground completely safe. Furthermore, they never spawn inside Underground Cabins.
• Werewolves may only appear during full moons, but a single one is tough against an early hardmode player, with high knockback resistance and the ability to give a debuff that halts regeneration. What makes matters worse is that they're common enemies when they do spawn — they can easily swarm you, especially if you happen to be stuck in the middle of a blood moon. Better hope your home base is secure...
• Crimson/Corrupt and Hallowed Mimics. They tend to show up without warning, have immense health, and unlike the basic Mimic, they pose a huge threat as they deal massive damage and can jump through blocks. Given that these things show up underground, you'll likely have little room to dodge their crazy jumps and get mangled in the process. Thank goodness for the Keys of Light and Night that let you manually spawn these guys and fight them on your terms, as otherwise getting their drops would be a major chore.
• The Pirate Invasion has two particularly nasty enemies:
  • Pirate Captains can only spawn one at a time and are slow moving but they blend in well with the horde of other pirates and they attack with a combination gun/cannon that fires bullets at a rate equal to the minishark and then finishes off with a cannonball that deals 200 damage. To top it off, killing them spawns the Pirate's Curse, a Ghost Pirate that is immune to all debuffs, can fly, is immune to all traps, can pass through blocks and deals decent damage.
  • Pirate Crossbowers fire flaming arrows with surprisingly good accuracy and damage. Their lower rate of fire is mitigated by the fact that multiples of them can spawn, quickly filling the air with dangerous projectiles.

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