Golden Castle of Stromberg [BLRR-EN010] Secret Rare

Once per turn, during your Standby Phase, you must banish 10 cards from the top of your Deck, face-down (this is not optional), or this card is destroyed. During your Main Phase: You can Special Summon 1 monster that specifically lists the card "Golden Castle of Stromberg" in its text from your Deck. You cannot Normal Summon/Set the turn you activate this effect. You can only use this effect of "Golden Castle of Stromberg" once per turn. When your opponent's monster declares an attack: Destroy the attacking monster, and if you do, inflict damage to your opponent equal to half the ATK that monster had on the field.