Buff Immunity: a debuff that prevents buffs from being applied. Things like focus, attack/defense, heal over time. Wouldn’t stop heals, guardian shields, or a human shield from guarding (though it would prevent the defense bonus)
Advantage: a buff that guarantees the next hit will be a critical hit, after which the buff expires. Wouldn’t affect rushes. Useful synergy for guardians, confounding, collateral damage, disarming, etc
Crit chance down and crit damage up/down: self explanatory. We have a boost to crit buff, but no reduction debuff. We also have nothing that boosts or reduces the damage a crit does
Stagger: a debuff that makes it so that the next time you take damage, all turn meter is lost. Since turn meter isn’t an element of this game, you could make it so all AP is lost instead.
Buff removal: this is present in the game, but is relatively limited (e.g. remove defense, remove attack). SWGOH has characters who can remove all positive effects from the entire enemy team at once. Like a Bizarro Tripp
Assist: calls a random ally (or allies) that is able (not stunned or guarding) to use their basic attack. Wouldn’t gain AP for the assisting toon, but would allow their weapon and specialist skills to proc, and also any negative effects to proc from attacking the targeted enemy
I’m sure a bunch of these wouldn’t fit the meta. But a few would. Worth considering, at least.