CASCOONS

#013 Cascoon
The evolution of a poison type or poisoned caterpeallar pokémon, which is a healing cascoona rather than the normal metapod forms,

much like a weedlera or poison paras's kakuna state, which is also called a kaskoona, this heals and adapts the poisoned condition during metomorphosis, and is necessary anyway, to emerge the bug type not alone, but poison type butterfrea often called a dustox. If you see a venonet change into cascoon, chances are he wants to be something new...