In honor of Mega Rayquaza, I propose the following Mega evolution for the eventual Diamond/Pearl remake. I believe it falls in line with balancing regarding Mega Legendaries.
Sp. Defense: 300
Typeless. Instead of 4 moves and 1 ability, it has 4 abilities and 1 move.
Abilities: Wonder Guard, Huge Power, Magic Bounce, Mold Breaker
Moves: Apocalypse. Base power 240, typeless, supereffective against all types, can hit through detect/protect, fly, and all invulnerable/semi-invulnerable states. Hits all opponents. including pokemon in reserve, stored in the PC, in the Pokemon Bank, in the wild, you in real life, and your mother.