Ikoria: Lair of Behemoths

Mythos of Snapdax | Sorcery | | 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. | Seb McKinnon

Dirge Bat | Creature | Bat | Mutate {4}{B}{B} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Flash Flying Whenever this creature mutates, destroy target creature or planeswalker an opponent controls. | Paul Scott Canavan

Extinction Event | Sorcery | | Choose odd or even. Exile each creature with mana value of the chosen quality. (Zero is even.) | Filip Burburan

Mythos of Brokkos | Sorcery | | If {U}{B} was spent to cast this spell, search your library for a card, put that card into your graveyard, then shuffle. Return up to two permanent cards from your graveyard to your hand. | Seb McKinnon

Umori, the Collector | Legendary Creature | Ooze | Companion — Each nonland card in your starting deck shares a card type. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} any time you could cast a sorcery.) As Umori, the Collector enters the battlefield, choose a card type. Spells you cast of the chosen type cost {1} less to cast. | Jehan Choo

Titans' Nest | Enchantment | | At the beginning of your upkeep, surveil 1. (Look at the top card of your library. You may put that card into your graveyard.) Exile a card from your graveyard: Add {C}. Spend this mana only to cast a spell that's one or more colors without {X} in its mana cost. | Cliff Childs