Charizard made a cameo appearance in Ash Ketchum vs Charles Darwin.
Information on the cameo
Charizard is a Fire/Flying-type Pokémon that evolves from Charmeleon, which evolves from Charmander. Its species is the Flame Pokémon, and it is the final evolution of Charmander, one of the three starters you can choose from in the first generation of the Pokémon games. It is often considered one of the most popular Pokémon to date, after Pikachu.
Ash Ketchum previously owned a Charizard, originally catching it as a Charmander after saving it from its previous owner before evolving it into a Charizard. It would initially disobey him, costing him his win in the Indigo League, but would eventually come to respect Ash and obey him, until its release in the Charicific Valley. It has made numerous returns since to temporarily aid Ash, returning to the valley each time up until the end of his adventure in Unova, where Charizard would instead reside at Professor Oak's lab there after.
Appearance in the rap battle
Charizard appears in Ash Ketchum's first verse after the line, "Open my pockets and go," covering the screen with fire as it roars its name and flies across the screen. After it roars "Charizard!", Ketchum finishes the line by saying, "On your ass!"