Frisk, Covet, Knock Off, Life Orb recoil, if it used a move boosted by a Gem, Trick, Switcheroo, any item that gives a unique effect (Air Balloon, Leftovers, Shell Bell, etc.), if it's a Focus Sash/Band that activates, Weakness Policy with a super effective move, Metronome if the move power keeps going up, White Herb if stat changes are reset, Heavy-Duty Boots if no hazard damage is taken, Power Herb if a move like Geomancy is used in one turn, Mental Herb if it is freed from Encore and the like immediately, Black Sludge, Ring Target if you can hit it super effectively with moves it should be immune to, Flame/Toxic Orb if it's statused, Berries if the criteria takes effect, if the Pokemon needs a specific item to be in that form (Arceus, Silvally, Genesect, Mega Evolutions, more), Teatime if the opponent has a Berry, Corrosive Gas, if it used a Z-Move, things like the Absorb Bulb and Cell Battery taking effect, and probably more I'm not thinking of.
Unnerve/As One can be a very niche way to determine if an opponent has a Berry, but it's hardly reliable, as there's no guarantee it would have a Berry.