Butterfree

Butterfree (Japanese: バタフリー Butterfree) is a dual-type Bug/Flying Pokémon introduced in Generation I.
It evolves from Metapod starting at level 10. It is the final form of Caterpie.

Metapod

Metapod (Japanese: トランセル Trancell) is a Bug-type Pokémon introduced in Generation I.
It evolves from Caterpie starting at level 7, and it evolves into Butterfree starting at level 10.

Caterpie

Caterpie (Japanese: キャタピー Caterpie) is a Bug-type Pokémon introduced in Generation I.
It evolves into Metapod starting at level 7, who evolves into Butterfree starting at level 10.

Blastoise

Blastoise (Japanese: カメックス Kamex) is a Water-type Pokémon introduced in Generation I.
It evolves from Wartortle starting at level 36. It is the final form of Squirtle.
Blastoise is the version mascot of Pokémon Blue, appearing on the boxart.

Wartortle

Wartortle (Japanese: カメール Kameil) is a Water-type Pokémon introduced in Generation I.
It evolves from Squirtle starting at level 16, and evolves into Blastoise starting at level 36.

Squirtle

Squirtle (Japanese: ゼニガメ Zenigame) is a Water-type Pokémon introduced in Generation I.
It evolves into Wartortle starting at level 16, who evolves into Blastoise starting at level 36.
Along with Bulbasaur and Charmander, Squirtle is one of three starter Pokémon available at the beginning of Pokémon Red, Green, Blue, FireRed, and LeafGreen.
It is also available in Pokémon HeartGold and SoulSilver, after obtaining all sixteen badges and defeating Red.

Charizard

Charizard (Japanese: リザードン Lizardon) is a dual-type Fire/Flying Pokémon introduced in Generation I.
It evolves from Charmeleon starting at level 36. It is the final form of Charmander.
Charizard is the version mascot of Pokémon Red and FireRed Versions. It also makes an appearance on the Pokémon Ranger, Pokémon Stadium, and Pokémon Mystery Dungeon: Explorers of Sky boxarts.