Witchoil Automaton

AC 17 (natural armor)
HP 134 (18d10+36; bloodied 67)
Speed 20 ft.
Initiative Dex –2 (8), Insight +0 (10), Perception +0 (10)

Proficiency +3; Maneuver DC 16
Saving Throws Str +5, Dex –2, Con +2, Int –4, Wis +0, Cha –5
Damage Resistances bludgeoning, piercing, and slashing damage from nonmagical weapons
Damage Immunities necrotic, poison
Condition Immunities charmed, fatigued, frightened, paralyzed, petrified, poisoned
Senses darkvision 120 ft., passive Perception 10
Languages understands the language of its creator but can’t speak

Bleak Aura. The construct’s attacks smear you with witchoil, drawing you and those nearby toward the Bleak Gate. The automaton’s weapon attacks are magical, and some of the automaton’s attacks can afflict a creature with its Bleak Aura. At the start of the automaton’s turn, each afflicted creature and each creature within 10 feet of an afflicted creature takes 5 (1d10) necrotic damage. However, that creature’s weapon attacks count as magical for the purpose of harming the automaton. A creature can remove the Bleak Aura from itself by immersing in water, taking fire damage, or spending an action to wipe the oil off.
Witchoil Breach. The glowing runes go dark, and then the construct’s torso shatters, spraying forth gallons of searing witchoil. The suddenly hollow machine teeters, but catches itself on a mangled forelimb. When the automaton is first bloodied, its souleater engine ruptures in a powerful explosion. Each creature within 20 feet takes 10 (3d6) fire damage, or half as much if it succeeds a DC 14 Dexterity saving throw . Each creature in the area is afflicted by the automaton’s Bleak Aura. Thereafter, the automaton’s Speed increases to 40 feet, and it gains a climb speed of 40 feet, but it loses Witchoil Ward and its Witchoil Fist attack no longer inflicts a Bleak Aura.
Witchoil Ward. The dull etched runes on the construct flare brighter and brighter as you assail it with magic. Their light seems to slow projectiles. The automaton has advantage on saving throws against spells and magical effects. Ranged attacks against it that originate more than 20 feet away have disadvantage . If those attacks already have disadvantage from being at long range, they automatically miss.

ACTIONS

Multiattack. The automaton makes two attacks.
Witchoil Fist. Black oil leaks from the joints of its fist. Melee Weapon Attack: +8 to hit; reach 5 ft., one target. Hit: 9 (1d8+5) bludgeoning damage and the target is afflicted by the automaton’s Bleak Aura.
Smash Aside. It plows through creatures and hurls objects in its way. The automaton throws an object of up to Medium size. Ranged Weapon Attack: +8 to hit; range 20 ft., one target. Hit: 9 (1d8+5) bludgeoning damage. Special: If the automaton hit a Medium or smaller creature with its Witchoil Fist attack this turn, when it uses this attack it throws that creature. If it hits with the attack, the thrown creature also takes 9 (1d8+5 bludgeoning damage).

TECHNOLOGICAL WEAKNESSES

Cold Fragility (Engineering DC 13). The belly of the machine is searing hot metal, with all the stresses that entails. When the automaton takes cold damage, if any single attack deals 15 or more bludgeoning, piercing, or slashing damage to it in the next turn, this triggers Witchoil Breach (regardless of how many HP the automaton has) if it hasn’t already triggered.
Howl of Souls (Arcana DC 13). The spirits burning in the construct’s engine wail, but are too weak to break free. Magic that would heal the automaton instead deals an equal amount of damage. The restorative energy briefly empowers the souls in the witchoil engine, and they fight against the wards holding them in. The automaton’s Bleak Aura does no damage on its next turn.