Omnath, Locus of the Void

Devoid
When Omnath enters the battlefield, create The
Essence, a legendary 10/10 spirit creature token
with that is all colors and "At the beginning of
your end step, sacrifice this creature unless you
pay {c}{c}{c}{c}
If you would lose unspent mana, instead create
a 1/1 colorless eldrazi creature token with
"{t}, sacrifice this creature: add {c}."