Ambush while on top of your deck.
Card sounds may differ from in-game as they get updated.
Ambush - An ambush unit can be played at the end of the enemy player's turn, or any time they are attacking you. If you played against a Killer or Relic Weapon attack, an Ambush unit will jump in the way to block that attack.
Warp - You can see cards with Warp when they are on top of your deck, and you can play them as if they were in your hand.