Rayquaza is a Legendary Pokémon who first appeared in the Pokemon Games Ruby, Sapphire & Emerald.
Rayquaza in the Super Smash Brothers series
Rayquaza first appears in the jungle after Diddy goes to investigate a crashed Arwing. It comes out of the water and attacks the Arwing with Hyper Beam, the kidnaps Diddy. As it goes back in the Water Fox comes out of the Arwing and attacks Rayquaza sending it Backwards.
There is a possible chance that Rayquaza could be a Boss in the Subspace Emissary alongside Petey Piranha.