The complete Pokemon RBY pokedex, part 1

Pokémon Name: Metapod
Type: Bug
Classification: Cocoon Pokemon
Pokédex Number: 011
Ability: Shed Skin – 1/3 chance of healing user's status ailment each turn
Location Found:
D/P/P: Eterna Forest with FireRed inserted
HG: Routes 2, 30 and 31, Ilex Forest, National Park, Viridian Forest and via Headbutting trees
SS: National Park Bug-Catching Contest (Tuesdays, Thursdays and Saturdays only)
White: Route 12
Black: Trade, Poke Transfer

As any good caterpillar would do, Caterpie hides in a shell with plans of metamorphosing into something greater. Thus, you're momentarily left with Metapod, a punching bag Pokemon that can only raise its defense. But once the cocoon breaks, you get the early-evolving Butterfree.

Evolution: From Caterpie at 7, to Butterfree at 10