Archtempered Demonic Berserker (Vicious Mangler)

Reckless. At the start of its turn, the berserker can gain advantage on all melee weapon attack rolls during that turn, but attack rolls against it have advantage until the start of its next turn. Additionally, for that same duration, the berserker can make a bonus action to lift its maul out of the ground if stuck instead of a full action.

Flashpod Resistance. The berserker has advantage on being blinded by items or equipment, whether magical or not.

Multiattack. The berserker makes two attacks.

Maul. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 19 (4d6 + 5) bludgeoning damage + 1 necrotic damage.

Fist/Headbutt. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 11 (1d12 + 5) bludgeoning damage.

Demonic Slam. The berserker makes a maul attack against a target within reach. On a hit, the target takes an additional 9 (2d8) bludgeoning damage and must succeed on a DC 18 Strength saving throw or be knocked prone. On a miss, the berserker's maul slams into the ground, rendering it stuck in the earth. The berserker must use an action (or bonus action if Reckless) to pull the maul up out of the ground in order to use it again.