I think it's final blowup from Rayquaza C level X
Actually, it's not. There are many different attacks that can deal more damage.
Any move that requires the flip of a coin until you hit tails can technically deal infinite damage if you can keep getting heads.
The max, as it seems, is 200.
The answer is mega Charizard EX, X or Y. They can deal up to 300 damage. Also I THINK I saw a Groudon and Kyogre legend that dealt up to 600 damage.