Fellforged

Construct Nature. The fellforged doesn't require air, food, drink, or sleep.

Inhabiting Spirit. The fellforged is inhabited and animated by a specter. If the fellforged fails a saving throw against an effect that turns undead, the specter is expelled into an unoccupied space within 5 feet of the fellforged with the hp total it had before it was expelled. The specter otherwise uses the statistics of a specter.

Sunlight Sensitivity. While in sunlight, the fellforged has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Multiattack. The fellforged makes two Necrotic Slam attacks.

Necrotic Slam. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 9 (2d6 + 2) bludgeoning damage plus 9 (2d8) necrotic damage. If the target is a creature, it must succeed on a DC 14 Constitution saving throw or its hp maximum is reduced by an amount equal to the necrotic damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hp maximum to 0.

Burst Gears. The specter within the fellforged strains the construct's body, sending broken springs and gears flying. Each creature within 5 feet of the fellforged must make a DC 14 Dexterity saving throw, taking 7 (2d6) piercing damage on a failed save, or half as much damage on a successful one. Each time the fellforged uses this bonus action, its speed is reduced by 5 feet, and it can't use this bonus action if its speed is 0. Its speed returns to normal when it finishes a long rest.