If I use Hoopa's "Assault Gate" attack after I move it up to replace a Pokemon that was KO'd by an opponent's attack, does it do anything?
No, Hoopa was moved to the Active Spot during the opponent's turn, not during "this turn".
Assault Gate




x2
Assault GateIf this Pokémon didn't move from the Bench to the Active Spot this turn, this attack does nothing. This attack's damage isn't affected by Weakness.
It gathers things it likes and passes them through its loop to teleport them to a secret place.
If I use Hoopa's "Assault Gate" attack after I move it up to replace a Pokemon that was KO'd by an opponent's attack, does it do anything?
No, Hoopa was moved to the Active Spot during the opponent's turn, not during "this turn".