Mythos of Snapdax is a rare Sorcery card from Ikoria: Lair of Behemoths Promos (PIKO), collector number 24p. Current market price: $0.53 (foil $0.25), 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.