- The Ecco the Dolphin series is packed with hordes of these, given that a lot of it takes place under the ocean.
First Person Shooter
- Jazz Jackrabbit 2 has turtles on lifebuoys. Though they only appear in one level and there's about three of them.
- There's an underwater version of the Mettaur, which has scuba gear and stuff.
- In Metroid: Fusion, the X seem to be able to combine the forms of Space Pirates and some species of carnivorous fish to make Mer-Pirates.
- Yoshi's Island features a Shy Guy with an inner tube as well as Shy Guys dressed as pirates.
Role Playing Game
- There is this kind of Genesis Clone in Crisis Core, namely the ones which Zack beats with a parasol.
- In the Final Fantasy series, there is Final Fantasy I, Final Fantasy III, Final Fantasy V, Final Fantasy VI, Final Fantasy VII, and Final Fantasy X which have underwater dungeons, and thus, enemies appropriate to the area (sea urchins, pirahnas, octopuses, etc.)
- The standard Pigmask army is supplemented by Navy SQUEALs in the underwater area of MOTHER 3.
- Mini Robot Wars has the land-based stealth unit called the Mole. In the New Game+, it gets the ability to swim on the water surface!
"Ocean doesn't save you from Mole anymore; for it can swim now!"
- And then you get even worse news later- the Giant also gets the ability to travel Amphibiously.
- Snorkel Zombies, Ducky Tube Zombies, and Dolphin Rider Zombies in Plants vs. Zombies.
- Pretty much every Zombie from Big Wave Beach in Plants vs. Zombies 2: It's About Time is this, starting out from the water and eventually making it to the shore (with the exception of the Fisherman who always stays on the water).
Turn Based Strategy
- XCOM Terror From The Deep replaces the first game's aliens with a variety of aquatic aliens and altered Earth species. Most of them are also able to fight on land.
- The various Gundam shows typically have at least one type of mass-produced underwater mobile suits for the main Gundam to fight.
- The original Mobile Suit Gundam and its spinoffs' Gog, Acguy and Z'Gok.
- Mobile Suit Zeta Gundam's Zaku Marine, which was actually an unused design from the original series that never made it into the show, brought out of retirement for a decoy operation.
- Mobile Suit Gundam ZZ's Capule, which later appears in Turn A Gundam on the Earth forces side as the Kapool.
- Mobile Fighter G Gundam's Pescatore, a Mexican submersible MS which inexplicably has a face like a parrot.
- Mobile Suit Gundam Wing's appropriately named (for once) Cancer and Pisces.
- Mobile Suit Gundam SEED's UMF-4A GO Oh N and UMF-5 Zn O, with the later UMF-3 ASH functioning as somewhere between this trope and Elite Mooks.