Brimstone barbarians

Immutable Form. The barbarian is immune to any spell or effect that would alter its form.

Magic Resistance. The barbarian has advantage on saving throws against spells and other magical effects.

Magic Weapons. The barbarian weapon attacks are magical.

Death Burst. When the barbarian dies, it explodes in a burst of magma. Each creature within 5 feet of it must then succeed on a DC 14 dexterity saving throw or take 10(3d6) fire damage

Multiattack. The barbarian makes two maul attacks.

Maul. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) force damage.

Thunderous Strike (Recharge 6). The myrmidon makes one Maul attack. On a hit, the target takes an extra 10(3d6) thunder damage, and the target must succeed on a DC 14 Strength saving throw or be knocked prone.

barbaric Rage. 2/day. The barbarian has advantage on Strength checks and Strength saving throws, +2 damage to all melee weapon attacks, and resistance to all non-cold damage. The rage ends when the barbarian is defeated, or a minute elapses. At the end of the rage the barbarian can't move or take actions until after its next turn, as a wave of lethargy sweeps over it.