Shoal Kraken

Constellation — Whenever an enchantment you control enters, you may draw a card. If you do, discard a card.

Sleep of the Dead

Tap target creature. It doesn't untap during its controller's next untap step.
Escape—{2}{U}, Exile three other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Starlit Mantle

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature you control
When this Aura enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+1.

Stern Dismissal

Return target creature or enchantment an opponent controls to its owner's hand.

Stinging Lionfish

Whenever you cast your first spell during each opponent's turn, you may tap or untap target nonland permanent.

Commanding Presence

Human Soldier

Enchant creature
Enchanted creature gets +2/+2 and has first strike and "Whenever this creature deals combat damage to a player, create a 1/1 white Human Soldier creature token."

Sweet Oblivion

Target player mills four cards.
Escape—{3}{U}, Exile four other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Thassa, Deep-Dwelling

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature.
At the beginning of your end step, exile up to one other target creature you control, then return that card to the battlefield under your control.
{3}{U}: Tap another target creature.

Thassa's Intervention

Choose one —
• Look at the top X cards of your library. Put up to two of them into your hand and the rest on the bottom of your library in a random order.
• Counter target spell unless its controller pays twice {X}.

Thassa's Oracle

When this creature enters, 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.)

Thirst for Meaning

Draw three cards. Then discard two cards unless you discard an enchantment card.

Threnody Singer

Flash
Flying
When this creature enters, 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.)

Thryx, the Sudden Storm

Flash (You may cast this spell any time you could cast an instant.)
Flying
Spells you cast with mana value 5 or greater cost {1} less to cast and can't be countered.

Towering-Wave Mystic

Whenever this creature deals damage, target player mills that many cards.

Triton Waverider

Constellation — Whenever an enchantment you control enters, this creature gains flying until end of turn.

Theros Beyond Death