Continuous Trap
If an opponent’s monster declares an attack while you control a “Drone Sentinel” monster: Destroy that attacking monster and place 2 Sentinel Counters on this card. You can remove 3 Sentinel Counters from this card; Special Summon 1 “Drone Sentinel” monster from your Deck. If this card is destroyed and you control a “Drone Sentinel” monster: Set this card to your field.