Ikoria: Lair of Behemoths

Mythos of Nethroi | Instant | | Destroy target nonland permanent if it's a creature or if {G}{W} was spent to cast this spell. | Seb McKinnon

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

Jegantha, the Wellspring | Legendary Creature | Elemental Elk | Companion — No card in your starting deck has more than one of the same mana symbol in its mana cost. (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.) {T}: Add {W}{U}{B}{R}{G}. This mana can't be spent to pay generic mana costs. | Chris Rahn

Death's Oasis | Enchantment | | Whenever a nontoken creature you control dies, mill two cards. Then return a creature card with lesser mana value than the creature that died from your graveyard to your hand. {1}, Sacrifice Death's Oasis: You gain life equal to the highest mana value among creatures you control. | Grzegorz Rutkowski

Eerie Ultimatum | Sorcery | | Return any number of permanent cards with different names from your graveyard to the battlefield. | Jason A. Engle

Emergent Ultimatum | Sorcery | | Search your library for up to three monocolored cards with different names and exile them. An opponent chooses one of those cards. Shuffle that card into your library. You may cast the other cards without paying their mana costs. Exile Emergent Ultimatum. | Zack Stella

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

Indatha Triome | Land | Plains Swamp Forest | ({T}: Add {W}, {B}, or {G}.) Indatha Triome enters the battlefield tapped. Cycling {3} ({3}, Discard this card: Draw a card.) | Noah Bradley

Zagoth Triome | Land | Swamp Forest Island | ({T}: Add {B}, {G}, or {U}.) Zagoth Triome enters the battlefield tapped. Cycling {3} ({3}, Discard this card: Draw a card.) | Eytan Zana