Apep's Night of Demise
Activate while you control at least 1 Level/Rank 7 or higher DARK monster. Target 1 non-DARK monster on the field: Banish it, then your opponent banishes every copy of that card from their deck, hand, Extra Deck, field, and GY, then you take damage equal to that monster's original ATK. If there is a card in either player's banished pile when this card is activated: You lose the Duel.
I tried to balance it with some restrictions, but I'm not sure if it's very balanced right now.