Arpaxion

Amphibious. The arpaxion can breathe air and water. 

Blood Frenzy. The arpaxion has advantage on melee attack rolls against any creature that doesn't have all its hit points.

Creature Sense. The arpaxion is aware of the presence of creatures within 1 mile of it that have an Intelligence score of 4 or higher. It knows the distance and direction to each creature, as well as each creature’s Intelligence score, but can’t sense anything else about it. A creature protected by a mind blank spell, a nondetection spell, or similar magic can’t be perceived in this manner.

Magic Resistance. The arpaxion has advantage on saving throws against spells and other magical effects.

Biting Tentacles. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 20 (3d10 + 4) piercing damage plus 5 (1d10) psychic damage.  If the target is a creature, it is pulled 5 feet towards the arpaxion and is grappled (escape DC 15).  Until this grapple ends, the target is restrained, and the arpaxion can't bite another target.

Claws. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) slashing damage and the target must succeed on a DC 15 Strength saving throw or be knocked prone.

Extract Brain. The arpaxion makes a biting tentacles attack against a restrained creature it is grappling.  On a hit, the target takes 55 (10d10) piercing damage. If this damage reduces the target to 0 hit points, the arpaxion kills the target by extracting and devouring its brain.