Mythos of Snapdax is a rare Sorcery card from Ikoria: Lair of Behemoths Promos (PIKO), collector number 24s. Current market price: — (foil $0.97), TCGplayer market prices via Scryfall.
Each player chooses an artifact, a creature, an enchantment, and a planeswalker from among the nonland permanents they control, then sacrifices the rest. If {B}{R} was spent to cast this spell, you choose the permanents for each player instead.