The complete Pokemon RBY pokedex, part 8

Pokémon Name: Grimer
Type: Poison
Classification: Sludge Pokemon
Pokédex Number: 088
Ability: Stench and Sticky Hold
Dream World ability: Poison Touch
Useful Attacks: Sludge Bomb
Location Found:
D/P/P: Route 212 (Poke Radar)
HG/SS: Routes 16, 17, 18, Celadon City, Safari Zone (Marshland); Pokewalker - Town Outskirts
B/W: Poke Transfer

Grimer and Muk remind us a lot of Hedorah, a Godzilla villain from the '70s. Odds are you have no idea who that is, so we'll just say that Grimer's many poisonous attacks make it a truly annoying Pokemon to deal with. Evolution takes a while, but you'll have access to even nastier moves. Bonus - making Grimer your number one Pokemon will reduce the number of wild encounters.

Evolution: To Muk at 38