Rayquaza

Rayquaza is a legendary Pokémon in the Pokémon series. It is the mascot of the game Pokémon Emerald. It appears in the Subspace Emissary story of Super Smash Bros. Brawl. During the events of the story, it suddenly emerges from a lake after hearing Diddy Kong, who had been looking at the nearly-destroyed Arwing nearby. It attacks Diddy with Dragon Pulse and snatches Diddy in his claws. Diddy screams for help, whereas Fox McCloud, who managed to escape the damaged Arwing, leaped from the Arwing and broke Diddy free of Rayquaza's grasp using Fox Illusion. Rayquaza, furious, ends up using Dragon Pulse on McCloud, who deflects it with Reflector, flinging it back at Rayquaza, who falls back into the lake. McCloud and Diddy then end up fighting Rayquaza, resulting as the second main boss of the game. Some of its attacks involve burrowing into the ground then bursting upwards, or flying with great speed horizontally over the stage and sometimes dropping a Thunder attack. The player can beat it by attacking it around the head.

Trivia

 * Rayquaza is the only non-playable Pokémon AND non-Poké Ball Pokémon to get its own sticker.
 * Rayquaza never interacted with anyone from its own series, which is something that Petey Piranha, Porky, and Ridley did.