Rayquaza achieves its Mega Evolution in a unique way, but The Pokemon Company is keeping it a secret ‘til we find out for ourselves. Its evolved form’s ability, Delta Stream, brings in strong winds to change the weather; in addition, if Groudon or Kyogre gets brought out, Drought or Drizzle will not activate. On top of that, Flying-types will no longer fall victim to Electric or Ice attacks, as Rayquaza’s ability makes them hit normally instead of super-effectively.
The Three Starting Types, by All.
Remember back when Game Freak thought it was a good idea to help us capture Regigigas in Platinum by giving us a level 100 Regigigas that unlocks Regirock, Regice, and Registeel so you can capture them to awaken the Regigigas in Snowpoint Temple that is now level 1 instead of 70?