Mega Rayquaza used Dragon Ascent.
"We have this Uber ass Pokémon being all cool and OP as hell, you know what it needs? Fucking more power. Hey, you know what? Let's give it a Mega Evolution WITHOUT NEEDING A STONE yeah that'll fucking show everyone who's the strongest Pokemon ever. Time to obliviate everything that comes in its path. Hmm, but what if it gets hit with a priority attack like Ice Shard? Oh, I know. Let's give it fuckng DeltA STREAM SO EVERY SUPER EFFECTIVE MOVE AGAINST IT SUCKS. Yeah great job Game Freak, let's see how much you still enjoy Wi-Fi battles with literally EvErYoNe using a Mega Rayquaza."