Mythos of Vadrok is a rare Sorcery card from Ikoria: Lair of Behemoths (IKO), collector number 127. Current market price: $0.19 (foil $0.19), 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.