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When the already Ubers-level Pokemon, Rayquaza, got a Mega Evolution, people fittingly freaked out. Its already sky high attack and special attack stats were jacked up to a ludicrous base 180, and its average 95 speed got boosted up to an excellent base 115. Its bulk also became quite good for such an offensive Pokemon. Let's also not forget its ability, Delta Stream, which was flat out broken. Aside from nullifying the effects of all weather, it simply removes all of Mega Rayquaza's weaknesses it has due to being a Flying type. It went from being neutral to Electric to resisting it, it was now neutral to rock (and also Stealth Rock, which is massive), and it was now only regularly weak to ice, as opposed to 4x weak to it. Finally (Yes, there's more) for its held item. "Wait," you might think. "Megas can hold items! They need to hold thier Mega stone to evolve. Well yes, but for Mega rayquaza, the rules of such primitive beings DO NOT APPLY. Rayquaza doesn't need a Mega Stone to evolve. It only needs to be able have the move Dragon Ascent in its movelist, which is a move it wanted to run anyways. Mega Ray proved to be too much for even the Ubers tier, so the community collectively agreed to ban it to a tier above Ubers, a tier now known as Anything Goes.