Magic Resistance.

The hellion has advantage on saving throws against spells and other magical effects.

Soul Taker.

A Giant or a Humanoid that is reduced to 0 hit points by the hellion dies, and its soul rises as a lemure (see the Monster Manual) on Avernus, one of the Nine Hells, in 1d4 hours. If the creature isn't revived before then, it can be restored to life only by a wish spell or by killing the lemure and casting true resurrection on the creature's original body.

Actions

Multiattack.

The hellion makes two Morningstar attacks.

Morningstar.

Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 20 (3d8 + 7) piercing damage plus 11 (2d10) fire damage. If the target is a creature, it can't regain hit points until the start of the hellion's next turn.

Infernal Orb.

The hellion hurls a magical ball of fire that explodes in a 20-foot-radius sphere centered on a point the hellion can see within 120 feet of itself. The sphere spreads around corners. Each creature in that area must make a DC 17 Dexterity saving throw. A creature takes 18 (4d8) fire damage and 18 (4d8) necrotic damage on a failed save, or half as much damage on a successful one.

Fire Hellion