Actions

Multiattack. The engine can use its Horrifying Presence and then make 2 bite attacks.   Steamy Bite. Melee Weapon Attack: +6 to hit, reach 5 ft ahead, one creature. Hit: 8 1d8+4 piercing + 11 2d10 fire damage.
Releases steam upon hit, akin to venomous fangs.   Horrifying Presence. Each creature of the engine's choice that can see it must succeed on a DC 16 Wisdom saving throw or become Frightened for 1 hour.
A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it.

Reactions

Stomp (opp attack only). All creatures on the sides of the pain engine must succeed on a DC 16 Dex save or take 13 2d8+4 bludgeoning damage.