Colimucus

X / Omega Ruby: It drives away opponents by excreting a sticky liquid that can dissolve anything. Its eyes devolved, so it can’t see anything.

Y / Alpha Sapphire: Its four horns are a high-performance radar system. It uses them to sense sounds and smells, rather than using ears or a nose.

Sun: It has trouble drawing a line between friends and food. It will calmly try to melt and eat even those it gets along well with.

Moon: This Pokémon’s mucous can dissolve anything. Toothless, it sprays mucous on its prey. Once they’re nicely dissolved, it slurps them up.

Ultra Sun: It crawls along sluggishly. The swirly protrusion on its back is filled with its brain and other organs.

Ultra Moon: Its entire body is covered with gooey mucus that can dissolve anything. Be sure to put gloves on if you’re going to touch it.

Sword: Although this Pokémon isn’t very strong, its body is coated in a caustic slime that can melt through anything, so predators steer clear of it.

Shield: The lump on its back contains its tiny brain. It thinks only of food and escaping its enemies.

Legends: Arceus: A creature given to melancholy. I suspect its metallic shell developed as a result of the mucus on its skin reacting with the iron in Hisui's water.