Blast Sphere (SBSC-EN027) [Speed Duel: Scars of Battle]

If this face-down Defense Position card was attacked by an opponent's monster, before damage calculation: Equip this card to the attacking monster. Then, during your opponent's next Standby Phase: Destroy the monster this card is equipped to, and if you do, inflict damage to your opponent equal to the ATK the destroyed monster had on the field.