Probably decent ones:
Ability Unity: OMotM from a while back, it allows a pokemon to use abilities from any other Pokemon sharing its type (regardless of order, so Normal/Flying = Flying/Normal). Quantity restricted to however many pokemon normally receive the ability for that type (eg. Rock/Flying has Defeatist from Archen and Archeops, so up to two Rock/Flying Pokemon on a team can have Defeatist)
<Plausibly add in ban for abilities obtained from above battling tier>
RainbowGen: Well, we already had RainbowTier.
Revisit Doubles/Triples: We had DUU, so how about a visit to DOU, or a Triples category? Triples with forced all Choice items gogogogo.
Suppression Cup: All Pokemon used must have a BST at or below... 520? 500? 480? Decide via matchups? Plausible ban on Choice, Evolite, and AV, as they provide immediate boosts.
BoringMons: aka you get a Pokemon and four moves. No IVs, EVs, or Nature, outside of those required for Hidden Power.
Bad/meme ones:
Also: