Swamp

Lotus Petal

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

River of Tears

{T}: Add {U}. If you played a land this turn, add {B} instead.

Exsanguinate

Each opponent loses X life. You gain life equal to the life lost this way.

Unearth

Return target creature card with mana value 3 or less from your graveyard to the battlefield.
Cycling {2} ({2}, Discard this card: Draw a card.)

Doomsday

Search your library and graveyard for five cards and exile the rest. Put the chosen cards on top of your library in any order. You lose half your life, rounded up.

Vampiric Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Priest of Gix

When Priest of Gix enters, add {B}{B}{B}.

Phenax, God of Deception

Indestructible
As long as your devotion to blue and black is less than seven, Phenax isn't a creature.
Creatures you control have "{T}: Target player mills X cards, where X is this creature's toughness."

Sunken Ruins

{T}: Add {C}.
{U/B}, {T}: Add {U}{U}, {U}{B}, or {B}{B}.

Underground Sea

Thassa's Oracle

When Thassa's Oracle 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.)

Sacrifice

As an additional cost to cast this spell, sacrifice a creature.
Add an amount of {B} equal to the sacrificed creature's mana value.

Necropotence

Skip your draw step.
Whenever you discard a card, exile that card from your graveyard.
Pay 1 life: Exile the top card of your library face down. Put that card into your hand at the beginning of your next end step.

Demonic Tutor

Search your library for a card, put that card into your hand, then shuffle.

Laboratory Maniac

If you would draw a card while your library has no cards in it, you win the game instead.