Spacegate (BP02-EN196) - Battle Pack 2: War of the Giants Unlimited

When a monster your opponent controls attacks or is attacked, place 1 Gate Counter on this card at the end of the Damage Step. During your Main Phase, you can send this card to the Graveyard to Special Summon 1 monster from your hand whose Level is equal to or lower than the number of Gate Counters on this card.