That poor Swampert
It was all but guaranteed that Rayquaza would be among those Pokémon in Omega Ruby and Alpha Sapphire to have a Mega Evolution — or perhaps a Primal Reversion, like Groudon and Kyogre — and as such it’s nice to get that confirmation out of the way.
Mega Rayquaza possesses Delta Stream, an ability that makes it so Flying-type Pokémon will only receive normal damage from moves they’d usually be weak to. Also, moves like Rain Dance and Hail and abilities like Snow Warning and Sand Stream will fail.
The new design is a big step up, I’d say. Regular Rayquaza’s lips always looked so silly to me.