History WakeUpCallBoss / Metroid

*** The Hive Mecha caused more trouble for some players than possibly all the other bosses combined. Here's the deal: you fight entirely from a circular platform in the middle of toxic water. The Ram War Wasps released by the Hive Totem circle you, and attempt to hit you. If they connect, you may very well fall into the water, which is hard to move around in (and therefore get out of), and which drains your energy extremely quickly. It also depends upon how good you are at quickly cycling between targets.

* ''VideoGame/AnotherMetroid2Remake'' throws the Ancient Guardian at you when you try to leave the Golden Temple and head to the second area of the game. It has four attacks that each have different "safe" areas to avoid them, it reacts to your movements which can sometimes make its attacks undodgable if they go off in the wrong spot, and the spiked walls steadily close in as you do damage. It also drops in without any warning in an area that was ''previously safe'', giving you no warning or preparation and if you don't figure out its quirks in time it'll easily kick your ass. It's also your first warning that this fan-remake is full of some nasty surprises that weren't in the original ''VideoGame/Metroid2ReturnOfSamus'' and that you'd better be on your toes.

* From the ''Franchise/{{Metroid}}'' series:
** ''VideoGame/MetroidFusion'' has three:
*** The first third has been relatively easy thus far, SA-X encounters aside. Then comes the B.O.X. Security Robot, who right away tries a DynamicEntry and is invulnerable while attacking. To damage it, Samus has to hang from monkeybars on the ceiling and shoot down into its core, which is easier said than done - particularly as all of the robot's attacks are all designed to knock you off the ceiling to get trampled by the thing.
*** In the second third, after exiting with the Power Bombs from Sector 5 (ARC), the power goes completely out. Thus begins possibly the hardest section of the game, with no save points between your ship and the save point on the other side of the boss battle. And between you and the boss battle are X-infected Ki-Hunters and Space Pirates that do lots of damage to you if they hit you. But then there's the boss itself. A giant spider who utilizes space-jump biology, it likes to spit fire into the corners and center of the room and then bounce from wall to floor to wall in an attempt to grab you. If it does, it will sap your health, lift you up, and slam you down for massive damage. The second phase of the fight involves it space-jumping around you and dropping bombs on you. It does this so fast, the most effective strategy is literally to just fire missiles upward or at an angle and hope they hit.
*** Then, to usher in the difficulty spike in the last portion of the game, is [[ThatOneBoss the Nightmare]]. After the punishing Yakuza battle and after defeating Nettori, there's a bit of a break in terms of difficulty, as enemies go down very easily and save points are readily available again. Until now. There's no real run-up like there was with the Yakuza, as the save point isn't that far from the boss chamber, but he doesn't need it. If you don't have enough energy tanks or missiles, good luck. The boss is able to manipulate gravity, but it refrains from doing so at first, instead firing a salvo of lasers at you every so often. Once you hit its gravity engine a few times, the gravity manipulation begins, and it feels like you are underwater, and you still have to hit the gravity engine at this low speed. Once you've destroyed the gravity engine, its mask pops off and you have to shoot its face full of missiles. Only catch is ''it tries to ram you while it does so'' as it just floats around the room at high speed to try to hit you some more.
** ''VideoGame/MetroidPrimeTrilogy'':
*** In the first game, the Hive Mecha caused more trouble for some players than possibly all the other bosses combined. Here's the deal: you fight entirely from a circular platform in the middle of toxic water. The Ram War Wasps released by the Hive Totem circle you, and attempt to hit you. If they connect, you may very well fall into the water, which is hard to move around in (and therefore get out of), and which drains your energy extremely quickly. It also depends upon how good you are at quickly cycling between targets.
*** From the same game, there's Flaahgra, the plant-monster main boss of the Chozo Ruins. In addition to a ring of toxic water like the one described above, Flaahgra features hard-hitting attacks from its scythe-like arms, the ability to shoot projectiles, AND the power to create an impossible-to-pass wall of plants that hurts you on contact. It's also the first boss that requires a strategy beyond "shoot its weak point": you have to run around the room and hit the large mirrors that are directing sunlight onto the monster to temporarily stun it and give yourself a chance to attack its root system in Morph Ball mode. The problem? Flaahgra ''knows'' about this weakness and, if you're too slow, will flip the mirrors back into place, meaning you have to go back to redo each one (and thus give the plant even more time to flip other mirrors). Furthermore, each round of the battle adds an extra mirror, each of which requires either multiple shots, a single Charge Shot, or a Missile blast--all while you're trying to avoid the huge monster that's swinging at you constantly. You can temporarily stun Flaahgra by firing either the Charge Shot or Missiles, but if you haven't found the former or are skimping on exploring and getting Missile Expansions for the latter, you're in for a nasty surprise. In short, unless you come into the battle well-equipped and having perfected techniques like strafing and dodging, you're going to be plant food--multiple times.
*** ''Prime 3's'' 5AM call from a swarthy hotel receptionist is Mogenar. Being the fifth boss of the game (after ''[[TheDragon Ridley]]'', for Pete's sake), yet still being the first ''Leviathan Guardian'', Mogenar demands a canny amount of accuracy, athletics, and downright suicidal bombing runs on his feet. Heck, Mogenar descends into ThatOneBoss territory for some people: Harder than anything that has come before, and a damn sight harder than anything that appears later.
*** In ''Prime 2'', the Splinter fight in the Great Temple will wake your ass up. It's a three-stage SequentialBoss; the first form is five Dark Splinters, the second an Alpha Splinter, and the third is the Dark Alpha Splinter. The first and third fights are laughably easy if done right, but if you haven't ''mastered'' circle strafing and dodging, the second form of that fight will tear you apart.
*** Also in ''Prime 2'', there's Amorbis, the fifth overall boss yet still the first of the Temple Guardians, and therefore the first of ''many'' MarathonBoss opponents you will face across the game. The reason for this is because you actually have to defeat ''six'' giant worms in order to score victory. And good luck figuring out the requirement of the Morph Ball to ultimately defeat them without using a guide. Ironically, they become one of the easiest bosses if you decide to play a [[SelfImposedChallenge No Dark Suit run]] by using a Ghetto Jump to [[SequenceBreaking Sequence Break]] into Torvus Bog.[[note]] A No Dark Suit run only lasts until you acquire the Light Suit, which is normally obtained late in the game.
*** One unique example in ''Prime 2'' is the Spider Guardian. The player will likely be comfortable with locking on and shooting enemies up until this point, and then the game flips its script and has a boss exclusively in morphball mode. If you aren't good at bomb jumping, boosting, and stopping in a specific area including up ramps with the morphball's less than precise ball physics, this boss will be a massive source of frustration.

*** Also in ''Prime 2'', there's Amorbis, the fifth overall boss yet still the first of the Temple Guardians, and therefore the first of ''many'' MarathonBoss opponents you will face across the game. The reason for this is because you actually have to defeat ''six'' giant worms in order to score victory. And good luck figuring out the requirement of the Morph Ball to ultimately defeat them without using a guide. Ironically, they become one of the easiest bosses if you decide to play a [[SelfImposedChallenge No Dark Suit run]] by using a Ghetto Jump to [[SequenceBreaking Sequence Break]] into Torvus Bog.[[note]] A No Dark Suit run only lasts until you acquire the Light Suit, which is normally obtained late in the game.[[/note]]