https://3ds.pokemon-gl.com/information/f4dfc61a-7f85-4e79-b305-ef63c1ceca3c (JP side, put up a week before the season went live)
https://3ds.pokemon-gl.com/information/dc05eac3-b309-4a73-a57c-42c90198b030 (EN side, put up the same day it went live)
Season 15, beginning next week, will be a really wacky one. Single battles (bring up to 6, pick 1), all moves except Metronome are banned. Mewtwo, Dusclops, and Dusknoir are also banned (for being uber in the first case, but more relevantly for having access to Pressure and shrinking everyone's PP supply that much further), as are mega stones.
Previous-gen transfers are allowed, and are pretty much mandatory to be able to fill out a full team--of course, unlike Smogon's own Metronome format, you're limited to legal sets. Get those duped TM35s from RBY ready.
It doesn't look like there's any prohibition on using Z-Metronome, if you want to basically change your ability to super-Sheer Force for a turn in case you roll an attacking move there. Or you could simply bring Assault Vest Machamp and take all the dice-rolling out of your equation, just jump right to Struggle. Note that gen 7 changed the mechanics of Choice items a bit: if your Metronome calls a 2-turn move like Sky Attack or Dig, it will fail on the second turn (as you're supposed to be choice-locked into Metronome, not Dig), so maybe that possibility is enough of a discouragement to drive you away from using those items. Metronome (the item) doesn't work here at all, unless you get extremely lucky and call the same move multiple times in a row.