Swamp

Frightcrawler

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
Threshold — As long as seven or more cards are in your graveyard, Frightcrawler gets +2/+2 and can't block.

Dauthi Horror

Shadow (This creature can block or be blocked by only creatures with shadow.)
Dauthi Horror can't be blocked by white creatures.

Howl from Beyond

Target creature gets +X/+0 until end of turn.

Gloom

White spells cost {3} more to cast.
Activated abilities of white enchantments cost {3} more to activate.

Stromgald Cabal

{T}, Pay 1 life: Counter target white spell.

Deathgrip

Order of the Ebon Hand

Protection from white
{B}: Order of the Ebon Hand gains first strike until end of turn.
{B}{B}: Order of the Ebon Hand gets +1/+0 until end of turn.

Unholy Strength

Enchant creature
Enchanted creature gets +2/+1.

Dread of Night

Knight of Stromgald

Protection from white
{B}: Knight of Stromgald gains first strike until end of turn.
{B}{B}: Knight of Stromgald gets +1/+0 until end of turn.

Sinister Strength

Enchant creature
Enchanted creature gets +3/+1 and is black.

Dunerider Outlaw

Protection from green
At the beginning of each end step, if Dunerider Outlaw dealt damage to an opponent this turn, put a +1/+1 counter on it.

Execute

Destroy target white creature. It can't be regenerated.
Draw a card.

Black Knight

First strike (This creature deals combat damage before creatures without first strike.)
Protection from white (This creature can't be blocked, targeted, dealt damage, or enchanted by anything white.)

Eastern Paladin

{B}{B}, {T}: Destroy target green creature.

Western Paladin

{B}{B}, {T}: Destroy target white creature.

Stench of Evil

Destroy all Plains. For each land destroyed this way, Stench of Evil deals 1 damage to that land's controller unless they pay {2}.

Slay

Destroy target green creature. It can't be regenerated.
Draw a card.

Deathmark

Dross Golem

Affinity for Swamps (This spell costs {1} less to cast for each Swamp you control.)
Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)

Talara's Bane

Target opponent reveals their hand. You choose a green or white creature card from it. You gain life equal to that creature card's toughness, then that player discards that card.