Nagash, God of Death

Eminence—If Nagash, God of Death is in the
command zone or on the battlefield, for each {1} in the cost of a Ossiarch Creature spell, you
may pay 1 Bone Tithe counter instead of pay
that mana.
Nine Books of Nagash—Lore of Death spells you
cast cost {1} less to cast for each Bone Tithe
counter you have.