Select 1 face-up card in the Spell & Trap Card Zones and destroy it. The controller of the destroyed card can then Set 1 Spell or Trap Card from their hand. If this Set card is destroyed and sent to the Graveyard, select and destroy 1 face-up card on the field.
Seems bugged considering it is supposed to only destroy monsters if the trap is destroyed while set, but even when it's activated and destroys a spell/trap it then destroys a monster when it leaves the field. Please fix otherwise it's an OP bugged card. Should only be able to destroy monsters if it is destroyed when set, not when it's active and destroyed because it was used.
I had this card set, ended my turn. Opponent had Ancient Gears, with Castle spell card face up. Why couldn't I trigger it when they drew a card, or in the standby phase? Then they summon Ancient Gear Golem, and it was too late.