8. Grimer
If we ignore the more…outlandish Pokédex entries (like Diamond and Pearl‘s “It was born when sludge in a dirty stream was exposed to the moon’s X-rays.”– which is, quite frankly, either a 1960s Marvel Comic origin story or the plot of classic B-Movie “The Blob”), Grimer is still quite a freaky-creepy creature. One can assume, that like its sort-of-cousins Garbodor and Trubbish, it’s basically rubbish that has gained sentience due to the buildup of mould, mildew and bacteria. That’s horrific in itself, but what’s worse is that it then feeds on other waste products from factories. “That’s a good thing, consuming our waste!” I hear you cry. Well, it would be good except for the fact that wherever Grimer moves, plants can never grow again.
Oh, one other thing: bits of its…body (can it be called a body?) fall away in its trail and they turn into other Grimer. Potentially, the Earth could be overrun with this poisonous slime, as it reproduces asexually, and contaminates the ground it slithers across. Muk, on the other hand, evades this list as it can actively control its internal toxins. It may be able to pollute a lake instantly, but its self control prevents it from being a danger. Oh, and its footprint only makes the ground barren for three years, which is significantly less than FOREVER. Grimer has no such control over its abilities. Who says that Pokémon doesn’t have a hidden message? GO GREEN, PEOPLE! RECYCLE AND…stuff.