Nemesis Prime, the Darkest

Hexproof. Indestructible.
Each upkeep, each opponent puts the top {x} cards of his/her library into his or her
graveyard, where {x} is the number of constructs
you control.
At the beginning of your end step, return all creatures in all graveyards to the battlefield under
your control as colorless construct creatures in addition to other types.