Mythos of Vadrok is a rare Sorcery card from Ikoria: Lair of Behemoths (IKO), collector number 324. Current market price: $0.36 (foil $0.86), TCGplayer market prices via Scryfall.
Mythos of Vadrok deals 5 damage divided as you choose among any number of target creatures and/or planeswalkers. If {W}{U} was spent to cast this spell, until your next turn, those permanents can't attack or block and their activated abilities can't be activated.