Baron of Hell

Unstoppable Fury.
If the Baron of Hell is reduced to half its hit points or fewer, it enters a rage-like state, gaining advantage on melee attack rolls and resistance to all damage (except radiant and psychic) for 1 minute.

Demonic Fortitude.
The Baron has advantage on saving throws against being paralyzed, stunned, or knocked prone.

Legendary Bulk.
The Baron counts as one size larger when determining carrying capacity and for grapple or shove checks.

Multiattack.
The Baron makes two melee attacks.

Infernal Fist (Melee Weapon Attack).
+9 to hit, reach 10 ft., one target.
Hit: 21 (3d10 + 6) bludgeoning damage plus 7 (2d6) fire damage. If the target is a creature, it must succeed on a DC 16 Strength saving throw or be knocked prone.

Hellfire Wave (Recharge 5–6).
The Baron stomps the ground and sends a wave of flame in a 30-foot cone. Each creature in the area must make a DC 16 Dexterity saving throw, taking 36 (8d8) fire damage on a failed save, or half as much on a successful one. Creatures who fail are also pushed back 10 feet and ignited, taking 5 (1d10) fire damage at the start of their turns for 1 minute (can be extinguished with an action).

Infernal Roar (1/Day).
When the Baron is hit by a critical hit or reduced below half HP, it can unleash a roar. Each creature within 30 feet must succeed on a DC 15 Wisdom saving throw or be frightened until the end of their next turn.