Embodiment of Dread

Enchant graveyard
Enchanted graveyard is a 1/1 creature with menace and indestructible.
Enchanted graveyard gets +X/+X, where X is the number
of cards in it.
Whenever enchanted library attacks, mill cards equal to its power.
If enchanted graveyard would leave the battlefield, instead destroy this enchantment, and you may cast any number of spells from it without paying their mana costs.

An inexorable force born from the unending certainty of death.