Banish the Otherworldly

Super split second (You may cast this spell while an effect or spell is resolving, interrupting its effect, and as long as this spell is on the stack, players can't cast spells or activate abilities that aren't mana abillities.)
Target opponent reveals their sideboard. Place a banishment counter on a card in exile or a card in a sideboard. As long as that card has a banishment counter, it cannot leave the zone it is in.