Notes:

http://www.smogon.com/forums/threads/ubers-is-now-a-tier-a-new-metagame-called-anything-goes-is-added-m-ray-is-banned-from-ubers.3523205/

- Ubers is now the name for the tier above OU. It is no longer just a banlist.
- We are adding a new metagame called Anything Goes (AG). AG has no bans, and no clauses, except for Endless Battle Clause. AG is the spiritual successor to (old) Ubers.
- Mega evolving Rayquaza will not be possible in the Ubers metagame.

What are some criteria for banning things from Ubers? We don't quite know yet, but here are some warning signs:
This Pokemon/ability/etc unreasonably raises the volatility of Ubers. Think Moody or OHKO spam.
This Pokemon is unreasonably centralizing. Think 70%+ usage. Even Xerneas was (I think) ~45% usage.
Related to the above point: This Pokemon is obviously in a different power bracket than most of the other Ubers. I argued earlier that M-Ray was in a different power bracket because it is the first ~800 BST Pokemon with a useful ability and unrestricted item.
It is no fun to play or watch matches with this Pokemon/ability/etc (henceforth just Pokemon) allowed. Having this Pokemon in Ubers makes me want to play some other meta. I would be bored as f--- to watch a match with this Pokemon allowed. This is a subjective criterion, but an important one I think: if everyone hates Ubers, then why have it? It is our obligation in such a case to try to fix it.