Check out Pokemon Omega Ruby and Alpha Sapphire's Mega Slowbro in action 

A video for the Mega-Evolved form of Slowbro was revealed today during the 2014 Pokemon World Championships in Washington, DC. It's below,

The gameplay trailer features Mega Slowbro in battle. The water and psychic-type possesses a ‘Shell Armor’ ability and one of two evolved forms of Slowpoke, the other being Slowking.

When Slowbro Mega Evolves into Mega Slowbro, its energy gathers in the Shellder clamped onto its tail. As a result, the hardness of its shell is boosted, making its armor incredibly strong. In battle, Mega Slowbro balances on its tail, wearing Shellder as an impenetrable armor over its body.

It also has the Shell Armor Ability, meaning opponents can never land a critical hit

Players can Mega Evolve Slowbro in Pokemon Omega Ruby and Alpha Sapphire November 21 on 3DS.