Swamp

Grasp of Darkness

Target creature gets -4/-4 until end of turn.

Unlikely Aid

Target creature gets +2/+0 and gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Demonic Embrace

Enchant creature
Enchanted creature gets +3/+1, has flying, and is a Demon in addition to its other types.
You may cast Demonic Embrace from your graveyard by paying 3 life and discarding a card in addition to paying its other costs.

Finishing Blow

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.

Serrated Scorpion

When Serrated Scorpion dies, it deals 2 damage to each opponent and you gain 2 life.

Fetid Imp

Flying
{B}: Fetid Imp gains deathtouch until end of turn. (Any amount of damage it deals to a creature is enough to destroy it.)

Walking Corpse

Gloom Pangolin

Lost Legion

When Lost Legion enters, 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.)

Skeleton Archer

When Skeleton Archer enters, it deals 1 damage to any target.

Underworld Sentinel

Whenever Underworld Sentinel attacks, exile target creature card from your graveyard.
When Underworld Sentinel dies, put all cards exiled with it onto the battlefield.

Blood Glutton

Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Goremand

As an additional cost to cast this spell, sacrifice a creature.
Flying
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
When Goremand enters, each opponent sacrifices a creature.

Demon of Loathing

Flying, trample
Whenever Demon of Loathing deals combat damage to a player, that player sacrifices a creature.