* BreatherBoss: Destructor. While he can be a DemonicSpider if you don't know how to destroy his missiles, once you learn that, he becomes a joke. He's also a big part in [[spoiler:getting a NoCasualtiesRun at the final battle.]]
* CrowningMusicOfAwesome: Some of the soundtrack in the game is rather amazing.
* DemonicSpiders:''Psychosquid.'' (aka the Type-P alien) It has very high health, moves faster than all of the aliens, eats multiple fish at once, and after some time, he goes into a defensive mode where he regains health if you shoot him.
** It gets worse when in tank 4, it attacks alongside Balrog.
** The Type-D alien, AKA Destructor, can be this for first-time players. [[GuideDangIt There's no indication you can shoot the missiles it launches]], and even all the offensive pets plus a max weapon can't kill it before it launches a round of missiles. So you'll be spending a lot of money to replace your fish before you learn how to destroy the missiles.
** Bilaterus. For one thing, [[AmbiguousGender he/she/it]] has to be killed ''twice'' to stop invading the tank. His spine also can eat fish, giving him a large hitbox for fish to be eaten by.
* DoNotDoThisCoolThing: Despite the game suggesting players to never shoot blue Psychosquid at any cost, it's actually a very good idea to shoot him when he's dangerously close to a fish you like.
* EnsembleDarkhorse: Blip. He can predict when your fish are hungry, where an alien will appear, and how much health an alien has left. That's all really cool, but his selling point is opening everything in the shop early. This allows you to prepare better for the first alien by buying extra lasers.
* FridgeBrilliance: Carnivores eat guppies, which cost 100 dollars. They drop diamonds, which give you 200, enough to buy two guppies. Same with ultravores, but multiply both values by 10. Coincidence? Unlikely.
* GoddamnedBats: All of the aliens unless you have Blip, since their attacks locations are unpredictable.
* SelfImposedChallenge: [[spoiler:In Sandbox Mode, summoning wadsworth, then summoning Ulysses (The Cyclops alien), then summoning a whole bunch of non-guppy fish. The goal is to try to get Ulysses's orbs to kill all of the fish. You can also add to this by putting in Angie.]]
* [[SidetrackedByTheGoldenSaucer Sidetracked By The Virtual Tank]]: Justified, since the shells you get from it can help you buy extra pets for the main game.
** [[spoiler:Sandbox mode might also count.]]
* StopHelpingMe: Blip in challenge mode. He opens everything in the shop early, making everything go up in price early on. This can break the game against your favor.
** Breeders. Once you get enough of them, they'll actually produce too many guppies.
* TearJerker: The end credits song,[[http://www.youtube.com/watch?v=w9scA_0ZKbY Lullaby]]. It's just so beautiful...
* TheScrappy: While Rhubarb is this In-Universe, most fans see Nostradomus as this. He produces snot which barely gives you any money, and guppies can eat them and turn into another Nostradomus. He also stops aliens via a [[HellIsThatNoise deafeningly loud sneeze]], which feels more like delaying the inevitable than an actual help.
** People are also not very fond of Gash, because he eats guppies, which includes adult guppies and [[spoiler:''royal guppies.'']]
** Although Blip is an EnsembleDarkhorse, he is bar none the '''WORST''' choice for Challenge mode. By opening the shop early, this also means items start to increase in price early, which hurts a lot in the long run.
* ViewerSpeciesConfusion: It's actually surprisingly common for people to mistake Psychosquid for an octopus, despite the fact that he's clearly a squid because of him having 6 tentacles, a coned head, and his name being Psycho''squid''.
* TheWoobie: Clyde. The sole reason he works for your tank is because he needs the money for his mother, who's in the hospital.