Ash's Quilava

Ash's Quilava is a -type Pokémon Ash caught in Johto that evolved from Cyndaquil shortly prior to the Lily of the Valley Conference.

Johto
As a Cyndaquil, similar to Ash's Charizard, Infernape, and Tepig, Quilava was forced to deal with an abusive trainer before Ash caught it, although unlike Charizard and Infernape it did not actually belong to that trainer.

At first, Cyndaquil had difficulty using its Fire type moves but eventually mastered Flamethrower and was capable of using it with such power that Jasmine's Steelix was roasted within its own Sandstorm.

Cyndaquil was used frequently in the Johto region and was left at Professor Oaks lab when Ash went to Hoenn.

Sinnoh
While training for the Sinnoh League, Ash brought Cyndaquil with many of his other Pokémon. However, Team Rocket tried to cause problems and Cyndaquil evolved into Quilava.

Quilava learned Eruption and was revealed to have learned Aerial Ace.

Voice actors and actress

 * Yūji Ueda (Japanese)
 * Kayzie Rogers (English as a Cyndaquil)
 * Bill Rogers (English as a Quilava)

Trivia

 * Quilava is Ash's first non-flying type Pokémon to know Aerial Ace.
 * It took Cyndaquil the longest of all of Ash's Pokémon to evolve.
 * So far, Quilava is the only one of Ash's fire types that did not evolve in its introduction series.