Careful Study

First-Sphere Gargantua

When First-Sphere Gargantua enters, you draw a card and you lose 1 life.
Unearth {2}{B} ({2}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Hapless Researcher

Sacrifice Hapless Researcher: Draw a card, then discard a card.

Counterspell

Ulamog's Crusher

Annihilator 2 (Whenever this creature attacks, defending player sacrifices two permanents of their choice.)
Ulamog's Crusher attacks each combat if able.

Cast Down

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Dispel

Horror of the Broken Lands

Whenever you cycle or discard another card, Horror of the Broken Lands gets +2/+1 until end of turn.
Cycling {B} ({B}, Discard this card: Draw a card.)

Hell Mongrel

Discard a card: Hell Mongrel gets +1/+1 until end of turn.
Madness {2}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Island

Dark Ritual

Mirrorshell Crab

Ward {3} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {3}.)
Channel — {2}{U}, Discard Mirrorshell Crab: Counter target spell or ability unless its controller pays {3}.

Swamp

Faultgrinder

Trample
When Faultgrinder enters, destroy target land.
Evoke {4}{R} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Gurmag Angler

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)

Lotus Petal

{T}, Sacrifice Lotus Petal: Add one mana of any color.

Pieces of the Puzzle

Reveal the top five cards of your library. Put up to two instant and/or sorcery cards from among them into your hand and the rest into your graveyard.

Striped Riverwinder

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Cycling {U} ({U}, Discard this card: Draw a card.)

Late to Dinner

Return target creature card from your graveyard to the battlefield. Create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this artifact: You gain 3 life.")

Dragon Breath

Enchant creature
Enchanted creature has haste.
{R}: Enchanted creature gets +1/+0 until end of turn.
When a creature with mana value 6 or greater enters, you may return Dragon Breath from your graveyard to the battlefield attached to that creature.

Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.