Other known variants
x2AmnesiaChoose 1 of the Defending Pokémon's attacks. That Pokémon can't use that attack during your opponent's next turn.
Swallow UpBefore doing damage, count the remaining HP of the Defending Pokémon and Swalot. If the Defending Pokémon has fewer remaining HP than Swalot's, this attack does 50 damage plus 30 more damage.
If my opponent has Celebi-EX with "Time Recall" in play, can I use Golduck's "Amnesia" attack to prevent the Defending Pokemon from using one of its previous evolution's attacks?
No, you can only use Amnesia on the attacks that are present on the opponent's card at the time of your attack.
If Wooper uses Amnesia on Scyther's Slash, then Scyther retreats for another Pokémon, then that Pokémon [is Switched] for Scyther again, can Scyther use Slash?
Amnesia references the defending Pokemon, when that Pokemon is benched the effect ends.