Homebrew

Traits

Magic Weapons. The Behemoth's weapon attacks are magical.   Regeneration. The Behemoth regains 10 hit points at the start of its turn if it has at least 1 hit point. If it takes Piercing damage it regenerates only 5 hit points.

Actions

Multiattack. The Behemoth makes three attacks: one with its bite and two with its claws.
Bite. Melee Weapon Attack: 1d20+9 to hit, reach 5 ft., one target. 1d8+5 piercing damage plus 3d6 psychic damage.
Claws. Melee Weapon Attack: 1d20+9 to hit, reach 5 ft., one target. 1d10+5 slashing damage plus 2d6 psychic damage.

Psionics. It uses its psychic abilities as spell like effects. It has a Spell save DC of 15.

Antagonize. It fills a target with rage and causes it to lash out to a target nearby. The creature makes a Wisdom Save DC15, on failure it takes 4d6 psychic damage and must make a melee attack against a creature in range, on success they take half damage and resist making an attack.

Mind Assault. The targeted creature's mind is filled with whispers and voices causing a major headache. The creature makes a Wisdom Save DC15, on failure it takes 3d6 psychic damage and has Disadvantage on its next attack. On success, it takes half damage.

Mental Feedback. Recharges on a 5 or a 6. All creatures within a 20 ft radius of the Behemoth must make a Wisdom Saving Throw DC15, on failure they take 3d6 psychic damage and their movement speed become 0 until the end of their next turn. On success they take half damage and only lose 10 feet of movement.