When this card is activated: Add 1 "Regulus, the Prince of Endymion" or 1 monster that mentions it from your Deck to your hand, then if your opponent controls a monster, you can Special Summon 1 Spellcaster monster from your hand. If a card(s) you control would be destroyed by battle or card effect, you can destroy 1 "Regulus, the Prince of Endymion" in your hand or face-up field instead. You can only use this effect of "Empire of Endymion" once per turn. You can only activate 1 "Empire of Endymion" per turn.