Underground Sea

Lotus Petal

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

Rain of Filth

Until end of turn, lands you control gain "Sacrifice this land: Add {B}."

Cabal Ritual

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if seven or more cards are in your graveyard.

Night's Whisper

Tendrils of Agony

Target player loses 2 life and you gain 2 life.
Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

Solve the Equation

Search your library for an instant or sorcery card, reveal it, put it into your hand, then shuffle.

Prismatic Vista

{T}, Pay 1 life, Sacrifice Prismatic Vista: Search your library for a basic land card, put it onto the battlefield, then shuffle.

Preordain

Scry 2, then draw a card. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Polluted Delta

{T}, Pay 1 life, Sacrifice Polluted Delta: Search your library for an Island or Swamp card, put it onto the battlefield, then shuffle.

Island

Brainstorm

Draw three cards, then put two cards from your hand on top of your library in any order.

Peer into the Abyss

Target player draws cards equal to half the number of cards in their library and loses half their life. Round up each time.

Swamp

Bloodstained Mire

{T}, Pay 1 life, Sacrifice Bloodstained Mire: Search your library for a Swamp or Mountain card, put it onto the battlefield, then shuffle.

Pact of Negation

Counter target spell.
At the beginning of your next upkeep, pay {3}{U}{U}. If you don't, you lose the game.

Thoughtseize

Target player reveals their hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

Flooded Strand

{T}, Pay 1 life, Sacrifice Flooded Strand: Search your library for a Plains or Island card, put it onto the battlefield, then shuffle.

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Dark Ritual

Duress

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

Scalding Tarn

{T}, Pay 1 life, Sacrifice Scalding Tarn: Search your library for an Island or Mountain card, put it onto the battlefield, then shuffle.