Death's Shadow

This creature gets -X/-X, where X is your life total.

Yargle, Glutton of Urborg

Rotting Regisaur

At the beginning of your upkeep, discard a card.

Shadow of Mortality

If your life total is less than your starting life total, this spell costs {X} less to cast, where X is the difference.

Leveler

When this creature enters, exile all cards from your library.

Eater of Days

Flying, trample
When this creature enters, you skip your next two turns.

Abyssal Persecutor

Flying, trample
You can't win the game and your opponents can't lose the game.

Colossus of Sardia

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
This creature doesn't untap during your untap step.
{9}: Untap this creature. Activate only during your upkeep.

Devouring Strossus

Flying, trample
At the beginning of your upkeep, sacrifice a creature.
Sacrifice a creature: Regenerate this creature.

Xu-Ifit, Osteoharmonist

{T}: Return target creature card from your graveyard to the battlefield. It's a Skeleton in addition to its other types and has no abilities. Activate only as a sorcery.

Metalwork Colossus

This spell costs {X} less to cast, where X is the total mana value of noncreature artifacts you control.
Sacrifice two artifacts: Return this card from your graveyard to your hand.

Colossus of Akros

Defender, indestructible
{10}: Monstrosity 10. (If this creature isn't monstrous, put ten +1/+1 counters on it and it becomes monstrous.)
As long as this creature is monstrous, it has trample and can attack as though it didn't have defender.

Kuro, Pitlord

At the beginning of your upkeep, sacrifice Kuro unless you pay {B}{B}{B}{B}.
Pay 1 life: Target creature gets -1/-1 until end of turn.