Theros Beyond Death

Protean Thaumaturge | Creature | Human Wizard | Constellation — Whenever an enchantment enters the battlefield under your control, you may have Protean Thaumaturge become a copy of another target creature, except it has this ability. | Izzy

Riptide Turtle | Creature | Turtle | Flash Defender | Brian Valeza

Stinging Lionfish | Enchantment Creature | Fish | Whenever you cast your first spell during each opponent's turn, you may tap or untap target nonland permanent. | Christopher Burdett

Thassa's Oracle | Creature | Merfolk Wizard | When Thassa's Oracle enters the battlefield, look at the top X cards of your library, where X is your devotion to blue. Put up to one of them on top of your library and the rest on the bottom of your library in a random order. If X is greater than or equal to the number of cards in your library, you win the game. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.) | Jesper Ejsing

Threnody Singer | Creature | Siren | Flash Flying When Threnody Singer enters the battlefield, target creature an opponent controls gets -X/-0 until end of turn, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.) | PINDURSKI

Towering-Wave Mystic | Creature | Merfolk Wizard | Whenever Towering-Wave Mystic deals damage, target player mills that many cards. | Jason Rainville

Devourer of Memory | Creature | Nightmare | Whenever one or more cards are put into your graveyard from your library, Devourer of Memory gets +1/+1 until end of turn and can't be blocked this turn. {1}{U}{B}: Mill a card. | Daarken

Mischievous Chimera | Enchantment Creature | Chimera | Flying Whenever you cast your first spell during each opponent's turn, Mischievous Chimera deals 1 damage to each opponent. Scry 1. | Antonio José Manzanedo