Stolen and rebuilt from the 4th edition hand book. Skull lords, to me, were an interesting monster. As the players damage the skull lord, the creature will consume its skulls to heal, limiting its future abilities in combat. I tested this out a couple of weeks ago on a very wary party. The withering flame came as a shock to dwarf fighter that was hit, as it consumed half of her total hit points.
Other than that, the heroes dispatched the creature quite easily. It probably didn't have a strong enough meat shield to protect it.
Skull Lord (CR 10)
Medium Undead, Lawful Evil
Armor Class: 18 Plate Armor
Hit Points: 60 (7d8+28) (see below)
Speed: 25 ft
Str 18 (+4), Dex 12 (+1), Con 18 (+4), Int 14 (+2), Wis 18 (+4), Cha 12 (+1)
Damage immunities: Poison, Necrotic
Condition Immunities: Exhaustion, poisoned
Senses: Darkvision 60 ft, passive perception 14
Turn immunity: The Skull Lord is resistant to the effects of turn undead
Death’s Chill: The skull lord radiates the power of death. Anyone within 10 feet of the creature takes 10 cold damage per turn.
Skull Healing: When a skull Lord is reduced to 0 hit points, one of its skulls is destroyed and the creature loses the related power. If the creature has any skulls remaining it instantly heals to 60 hit points. When all three skulls are destroyed, the Skull Lord is destroyed as well
Multiattack: The Skull Lord makes two staff of death strikes or uses a skull ability
Staff of Death: +8, 10 (1d10+4), the target makes a DC 18 constitution check and takes 14 (4d6) necrotic damage on a failed save or half as much on a successful one
Skull of Withering Flame: The skill lord launches a purple bolt of necrotic energy at a single target within 60 feet. The target creature must make a DC 18 dexterity save, taking 45 (10d8) necrotic damage on a failed save or half as much on a successful one
Skull of Bone Spurs: The skull lord fires 3 magic bone spurs at up to 3 targets. Bone Spur: +8 to hit, range 60 ft, 14 (4d6) damage
Skull of Death’s Command: The Skull Lord can raise a destroyed skeleton of CR 4 or below OR the skull lord can remove the effects of Turn undead on 2 creatures.