Black rare creature. Something you'll want to attack with (not a small utility creature like Royal Assassin / Dark Confidant / Will o the Wisp / Wall of whatever).
Let's start the voting!
Memoria Vampiris –
Creature – Vampire Wizard (R)Flying, hexproof
Mastery—When Memoria Vampiris enters the battlefield, if you control an artifact, a creature, an enchantment, and a land, gain control of target creature.
It wipes your memory of everything but its eternal whisper.4/4
Spectral Loner Creature—Spirit (R)
Haste
You may cast ~ from your graveyard.
When a player controls another creature, sacrifice ~.
When the world was made inhospitable to life, darker things prospered.3/1
Spirit of Cold Nights -
Creature - Spirit
Whenever ~ deals damage to an opponent, it deals that much damage to each tapped creature he or she controls.
Whenever ~ deals damage to a tapped creature, draw a card.
4/6
Demon of Ancient Misery
Creature-demon (R)
Flying, trample
Whenever [cardname] deals damage to an opponent, put a Relic artifact token onto the battlefield. (Relics have no abilities)
At the beginning of your upkeep, sacrifice an artifact or creature.
He remembers the pain of changing seasons, and he plans to inflict it again. 5/5
Treacherous Caravaneer Creature - Human Wizard (R)
When Treacherous Caravaneer enters the battlefield, put three 2/2 black Zombie creature tokens onto the battlefield, then sacrifice three creatures.
Although their zombies' food can be morally difficult to procure at times, necromancers enjoy impunity in the anarchy of the desert.4/3
Frostwind Lich Creature - Zombie WizardDeathtouch
At the end of each turn, if 3 or more creatures died this turn and ~ is in your graveyard, return it to the battlefield.
3/1
Undead Collector Creature - Zombie Wizard
When ~ enters the battlefield, you may exile up to one each of creature, artifact, enchantment, land and instant or sorcery cards from target opponent's graveyard.
Whenever a creature you control deals combat damage to a player, you may cast one of the exiled cards without paying its mana cost.
3/4
He covets many things in this world, foremost being the world itself. Lifesapper --
Creature - Plant (R)
Lifelink
At the beginning of your end step, if Lifesapper is untapped, you lose 5 life.
5 / 2
Soul Furnace Enchantment Creature - SpiritIntimidate
Surge —
, Exile two creature cards from your graveyard.
(You may cast ~ for its surge cost. If you do, it enters the battlefield with haste. Sacrifice it at the beginning of your next end step.)You may cast ~ for its surge cost from your graveyard.
3/2 Tunneling Rot Wurm
Creature - Zombie Wurm
~ is unblockable.
2/1
I vote for TPzombieW.