You take one extra move right away, and the enemy piece that moved last (king excluded) is stuck in the loop and cannot move on your opponent's next turn.
You draft Deja Vu in Buff mode. Free action: you choose when to use it, and it resolves without costing your turn.
As a tempo card, it buys time: an extra move, a skip, or a freeze.
“Haven't we... no. Surely not. Haven't we...”