Doom Blade

Gray Merchant of Asphodel

When Gray Merchant of Asphodel enters, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Nightveil Specter

Flying
Whenever Nightveil Specter deals combat damage to a player, that player exiles the top card of their library.
You may play lands and cast spells from among cards exiled with Nightveil Specter.

Underworld Connections

Enchant land
Enchanted land has "{T}, Pay 1 life: Draw a card."

Swamp

Temple of Silence

This land enters tapped.
When this land enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
{T}: Add {W} or {B}.

Mutavault

{T}: Add {C}.
{1}: Mutavault becomes a 2/2 creature with all creature types until end of turn. It's still a land.

Bile Blight

Target creature and all other creatures with the same name as that creature get -3/-3 until end of turn.

Hero's Downfall

Devour Flesh

Target player sacrifices a creature of their choice, then gains life equal to that creature's toughness.

Desecration Demon

Flying
At the beginning of each combat, any opponent may sacrifice a creature of their choice. If a player does, tap this creature and put a +1/+1 counter on it.

Thoughtseize

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

Pack Rat

Pack Rat's power and toughness are each equal to the number of Rats you control.
{2}{B}, Discard a card: Create a token that's a copy of Pack Rat.