I agree with what the above posters said. This metagame was originally made during early XY when they weren't banned yet. When I started to play this again with Articuno I, we kept the original banlist. The past few days we've thought about suspects to make the metagame healthy, and none of us really feel Deoxys-D, Deoxys-S, Aegislash or Landorus I are broken in this metagame, and they all help their teams. Mega Mawile was a bit more controversial, but we allowed it because of its low speed and vulnerability to special attacks, while it gives Defense teams some offensive presence.Snaquaza I'm not sure why some Ubers are allowed but I'd like you to consider putting this in line with OU. Usually OMs retroactively unban (or keep Ubers unbanned after OU bans them) because mechanics make them worse off versus other threats in the metagame. HSM doesn't offer new mechanics. Deoxys or Landorus or Mega Mawile are not worse here than in OU.
Thoughts?
We may ban any of them if they appear to be too good, although I'd prefer not to, to keep a stable metagame.