Mew-Ditto

Ditto is a failed Mew clone. If Ditto's DNA is polluted, it turns into sludge (Grimer). If Grimer stays moist, it evolves into Muk. If it dries out, it becomes a gas (Koffing), which evolves into Weezing. Now, if Grimer gets into a trash bag to stay moist,? it's body fuses to the bag and the bag becomes part of its body (Trubbish-Garbodor).