Black Mage-Eternal

Undead Fortitude. If damage reduces the Eternal to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the Eternal drops to 1 hit point instead.

Menace. The first time a creature starts it's turn within 10 feet of the Mage-Eternal, it must make a DC 13 Wisdom saving throw or be frightened of the Eternal for 1 minute. At the end of each of its turns, it can repeat the saving throw, ending the effect on itself of a success. If a creature succeeds on a saving throw against this ability, it is immune to this ability for 24 hours.

Sacrifice. Whenever the Mage-Eternal hits with an attack, it can deal 2d4 necrotic damage to itself. If it does, it also deals an equal amount of necrotic damage to its target.

Slam. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage.

Mana Bolt. Ranged Spell Attack: +5 to hit, range 30 ft., one target. Hit: 7 (2d6) necrotic damage.