At first this looked fun, but it seems like it's pure rush which is not fun. The most obviously potent threats are Set-Up and Weather.
Smeargle gets any broken set-up move and Mat Block. Most people know the first half: Geomancy, Shift Gear, Shell Smash, Z-Conversion, etc. The second half is something most people are probably not aware of. Mat Block is Greninja's signature move (until this gen where Throh got it) where, on the first turn the user comes in, both the user and the ally are protected. This allows the ally to do whatever the fuck they want. Set up a Geomancy? No problem. Set up a Z-Conversion? Sure. Set-up a Shell Smash? It's fine they're safe. This makes set-up everywhere as they can just switch in, be protected, then switch out. In addition, you can have up to 5 other mons with Geomancy or Shell Smash no problem. It would just be spam. In addition, Smeargle can also allow for other mons to get dream coverage moves. Give Greninja Blue Flare or Seed Flare, give Swoobat Dazzling Gleam or Moonblast for when a 260 BP stored power cant hurt a dark type. The list goes on (I know I'm using Geomancy a lot, but still). It basically turns it into this broken mess. Not fun.
Okay, you've banned Smeargle. You've only gotten rid of Geomancy and absurd coverage. You still have Porygon-Z, Genesect (yes its legal), Cloyster, etc. There's still plenty of abusers including the previously mentioned ones. Swoobat and Greninja are just as broken just now using White Herb instead of Power Herb. Swoobat still has 260 bp Stored Power at +4 / +4. Greninja still has all that coverage, Technician, and more at +2 / +2. This is not fun and will continue to be hell. I think that Geomancy, Shell Smash and Conversion/Happy Hour/Celebrate should be quick banned.
Next thing I think will be way too strong is weather. I don't want to deal with something like a Sand Rush Kartana, Swift Swim Volcanion, Sand Force Sand Veil Garchomp, basically shit that hits hard and fast. Excadrill, Kingdra, and Mega Swampert would be the most common for pretty clear reasons, but there would also be some that would pop up like Kabutops. It's just these powerful fast mons with moves boosted by weather. This isn't as broken as set-up, but it seems it will be centralizing and just turn into gen 5 weather wars after crazy set-up moves are banned.