Black Dragonforged Wurmcoil Engine

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 16 Wisdom saving throw or become frightened for 1 minute. 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, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Deathtouch. A creature hit by a melee weapon attack from the engine must succed a dc 22 dex save, taking 40(10d6) acid damage on a failed save. Half as much on a success. 

Perfected Lifelink. When a creature takes damage from one of it's attacks, it regains hp equal to the damage dealt.

Acid cannon (Recharge 5-6). The engine blasts acid in a 30-foot line that is 15 feet wide. Each creature in that line must make a DC 22 Dexterity saving throw, taking 64 (14d8) acid damage on a failed save, or half as much damage on a successful one.

Multiattack . The Engine makes three attacks. Two slams and one bite

Slam. Melee Weapon Attack: +15 to hit, reach 5 ft. one target. Hit: 32 (6d6 + 10) [magical bludgeoning] damage. 

Bite. Melee Weapon Attack: +15 to hit, range 15ft. one target. Hit: 50 (8d10 + 10) [magical piercing] +18(4d6) [Acid] damage.

Melee attack. Makes one melee attack when creature leaves it's space