Lifelink. When the engine damages a creature with a melee attack, the engine regains hitpoints equal to halve the damage dealt (rounded down).

Multiattack. The Engine makes three attacks, one with its bite, and two with its tail. If a creature is grappled by Bite, The Engine can use Shred instead of Bite. 

Bite. Melee Weapon Attack: +14 to hit, reach 5ft, one target. Hit:  22 (4d6 + 8) piercing damage. If the target is a creature, the creature is grappled and the engine can no longer use bite

Tail. Melee Weapon Attack: +14 to hit, reach 15ft, one target. Hit: 20 (3d6 + 8) bludgeoning damage.

Shred. Melee Weapon Attack: The engine makes one Bite attack against a creature it is grappling, if it hits, the target takes the Bite's damage + 15, the target is no longer grappled, and the target must make a constitution save (DC 18), or begin bleeding for 6 (2d4 + 2) damage per round, for 3 rounds, or until healed.