Ikoria: Lair of Behemoths

Archipelagore | Creature | Leviathan | Mutate {5}{U} (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.) Whenever this creature mutates, tap up to X target creatures, where X is the number of times this creature has mutated. Those creatures don't untap during their controller's next untap step. | Svetlin Velinov

Avian Oddity | Creature | Bird | Flying Cycling {2}{U} ({2}{U}, Discard this card: Draw a card.) When you cycle Avian Oddity, put a flying counter on target creature you control. | Simon Dominic

Pollywog Symbiote | Creature | Frog | Each creature spell you cast costs {1} less to cast if it has mutate. Whenever you cast a creature spell, if it has mutate, draw a card, then discard a card. | Simon Dominic

Pouncing Shoreshark | Creature | Shark Beast | Mutate {3}{U} (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 Whenever this creature mutates, you may return target creature an opponent controls to its owner's hand. | Dan Scott

Wingspan Mentor | Creature | Human Wizard | When Wingspan Mentor enters the battlefield, put a flying counter on target non-Human creature you control. {2}{U}, {T}: Put a +1/+1 counter on each creature you control with flying. | Sidharth Chaturvedi

Jubilant Skybonder | Creature | Human Wizard | Flying Creatures you control with flying have "Spells your opponents cast that target this creature cost {2} more to cast." | Jesper Ejsing

Cunning Nightbonder | Creature | Human Rogue | Flash Spells with flash you cast cost {1} less to cast and can't be countered. | Ekaterina Burmak

Lore Drakkis | Creature | Lizard Beast | Mutate {U/R}{U/R} (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.) Whenever this creature mutates, return target instant or sorcery card from your graveyard to your hand. | Lucas Graciano

Sprite Dragon | Creature | Faerie Dragon | Flying, haste Whenever you cast a noncreature spell, put a +1/+1 counter on Sprite Dragon. | Gabor Szikszai

Parcelbeast | Creature | Elemental Beast | Mutate {G}{U} (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.) {1}, {T}: Look at the top card of your library. If it's a land card, you may put it onto the battlefield. If you don't put the card onto the battlefield, put it into your hand. | Milivoj Ćeran

Trumpeting Gnarr | Creature | Beast | Mutate {3}{G/U}{G/U} (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.) Whenever this creature mutates, create a 3/3 green Beast creature token. | Aaron Miller