Sure, how about this:
Arcane Hunger - Dar'Khan steals X health and mana from nearby enemies and undead allies, healing himself and gaining increased damage for 10 seconds.
Dark Rebirth - raises a powerful skeleton warrior from target corpse. If Dar'Khan has the damage buff from Arcane Hunger, he raises a skeletal mage instead (same damage but with ranged attack and some minor spells - like Frost Armor or Frost Arrows - auto-cast things)
Lich King's Favor - sacrifices all skeletal warriors, granting Dar'Khan invulnerability, lasting X seconds for each skeletal warrior sacrificed. However, Dar'Kahn loses Y health per minion sacrificed when he casts this spell.
Anguish and Torment - (Ultimate) - sacrifices all skeletal minions, unleashing a devastating blast of energy at the target. If target dies from the spell, it hits another nearby enemy for half the damage (And so on, until it drops to zero damage).