An iron knight the size of a doorway: a blade for an arm that burns, a bolt of fire from range, and a cone of poison gas now and then. Fire only feeds it.
Languages: understands Common and two other languages but can't speak
Traits
Fire Absorption. Fire damage heals it instead: it regains Hit Points equal to the Fire damage dealt.
Immutable Form. It can't shape-shift.
Magic Resistance. Advantage on saving throws against spells and other magical effects.
Actions
Multiattack. Two attacks, Bladed Arm or Fiery Bolt in any combination (the engine plays two Bladed Arms in reach; Fiery Bolt is its attack from range).
Bladed Arm. Melee Attack Roll: +12, reach 10 ft. Hit: 20 (3d8 + 7) Slashing damage plus 10 (3d6) Fire damage.
Fiery Bolt. Ranged Attack Roll: +10, range 120 ft. Hit: 36 (8d8) Fire damage.
Poison Breath. Constitution Saving Throw: DC 18, each creature in a 60-foot Cone. Failure: 55 (10d10) Poison damage. Success: Half damage.
Where you meet it
Castle Ravenloft, the Brazier Room: The western knight steps into the pale light, shaking centuries of grey dust from its hinges. Its twin across…