Adamantine Construction. The Adamantine Hunter is immune to critical hits.

Liquid Form. The Adamantine Hunter is immune to any spells or effects that would alter its form. In addition, if the total for an attack roll against the Adamantine Hunter is 25 or greater, it is resistant to the incoming damage of the attack. If the attacker rolls a 20, their weapon becomes stuck in the Adamantine Hunter, requiring a DC 20 strength check to pull it free.

Magic Resistance. The Adamantine Hunter has advantage against spells and other magical effects.

Magic Weapons. The Adamantine Hunter’s weapon attacks are considered magical.

Faultless Tracker. The Adamantine Hunter is given a quarry upon activation. The hunter knows the direction and distance to its quarry as long as the two of them are on the same plane of existence. 

Multiattack. The Adamantine Hunter makes three slam attacks, then uses its arcane cannon if its available. If all three slam attacks hit the same person, the target must succeed on a DC 20 strength saving throw, or be knocked 20 feet away from it and knocked prone.

Slam. Melee weapon attack. +12 to hit, reach 10 ft. Hit. 27 (3d12 + 7)

Arcane Canon (Recharge 6). Ranged Spell Attack. +9 to hit, range 120/300. 2 attacks Hit: 18 (4d8) force damage