* BreatherBoss: There are more of them than not, if you use the proper tactics and weapons (usually a well placed Laser Sword of some sort, but not always).
** Special mention goes to red [[MacrossMissileMassacre Bombardier]] at the end of Corridor 21, he is fought at the end of the BossRush right after [[ThatOneBoss Grimgrin]] and before [[FinalBoss It]].
* DemonicSpiders: In the last few corridor levels, there is a blue ship enemy that [[BeamSpam loves to fire lasers]]. Each laser does more damage than any of the bosses can do to your character, even after having all the armour upgrades. The fact that this enemy comes is large numbers doesn't help, either...
* GoddamnedBats: Many of the small mooks, especially the various [[PaletteSwap multicoloured jumping jellies]] in the labyrinth stages, as well as countless types of enemies in the Corridor stages. The labyrinth areas have bats, but those are not the enemies you should be worrying about.
* GoodBadBugs: If you have enough chips, you can buy all of the items in the shops where the Blue Landers are offering you multiple objects for sale by pausing very quickly as you make your first purchase.
* NightmareFuel: A few of the bosses, but Grimgrin especially. Although his normal form -- a freakish floating head with lots of eyes-- is already creepy, it reaches a whole new level as your attacks [[EyeScream blow out his eyes, leaving gaping sockets]]...and then a flood of tiny, damaging eyeballs pour out from them, filling the screen.
* SuspiciouslySimilarSong: [[http://www.youtube.com/watch?v=iYH7pRottu8 The intro stage's music]] sounds suspiciously similar to [[http://www.youtube.com/watch?v=YwDzQROcDNA the overworld theme of]] ''[[ZeldaIITheAdventureOfLink Zelda II: The Adventure of Link]]''.
* ThatOneBoss: [[NightmareFuel Grimgrin, the monster with the]] [[ExtraEyes mass of eyes]]... [[TurnsRed and it bombards ''more of them'' at you as they take damage]]. The FinalBoss, It, does the same thing, in addition to having CombatTentacles, which make it harder to attack from the front. And it's got homing missiles too.
** On the surface-traveling stages, the jumping balls of seaweed, especially the [[PaletteSwap blue and red ones]]. And then there's also the one-time-only "dinosaur skull" miniboss and "ice crystal" miniboss, both of which spam homing projectiles and do ludicrous amounts of damage to you.
** There's also Optomon, the boss that looks like a tangled lump of seaweed with an eye in the middle. They also fire long lines of vines that will inflict an unbelievable amount of damage to you in a short amount of time if you get caught by them. The green one is mildly challenging, but the blue one is very, ''very'' tough to beat. By the time you get to the red one, however, you're much stronger and better prepared to deal with it, so while still challenging, it's not as hard.