Nightmare

Flying (This creature can't be blocked except by creatures with flying or reach.)
Nightmare's power and toughness are each equal to the number of Swamps you control.

Sengir Vampire

Flying (This creature can't be blocked except by creatures with flying or reach.)
Whenever a creature dealt damage by Sengir Vampire this turn dies, put a +1/+1 counter on Sengir Vampire.

Skeleton Archer

When this creature enters, it deals 1 damage to any target.

Vampire Opportunist

{6}{B}: Each opponent loses 2 life and you gain 2 life.

Swamp

Eternal Thirst

Enchant creature
Enchanted creature has lifelink and "Whenever a creature an opponent controls dies, put a +1/+1 counter on this creature." (Damage dealt by a creature with lifelink also causes its controller to gain that much life.)

Compound Fracture

Target creature gets -1/-1 until end of turn. It gets an additional -1/-1 until end of turn for each card named Compound Fracture in your graveyard.

Demon of Loathing

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

Bad Deal

You draw two cards and each opponent discards two cards. Each player loses 2 life.

Cruel Cut

Destroy target creature with power 2 or less.

Unlikely Aid

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

Savage Gorger

Flying
At the beginning of your end step, if an opponent lost life this turn, put a +1/+1 counter on Savage Gorger. (Damage causes loss of life.)

Murder

Mardu Outrider

As an additional cost to cast this spell, discard a card.

Sanitarium Skeleton

{2}{B}: Return Sanitarium Skeleton from your graveyard to your hand.

Malakir Cullblade

Whenever a creature an opponent controls dies, put a +1/+1 counter on Malakir Cullblade.

Typhoid Rats

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)