Wriggling Biter

Abomination's Ruinous Physique. The Biter regains 10 hit points at the start of its turn. If the Biter takes radiant damage, in regains no hit points at the start of its next turn. The Biter dies only if it is reduced to 0 hit points by radiant damage or takes radiant damage while at 0 hit points.

Abominous Resistance. Whenever the Biter would make a saving throw against a spell or another magical effect it can choose to make a Constitution saving throw instead of whatever saving throw the effect calls for.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 10 (1d12+4) piercing damage.

Constrict. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 7 (1d6+4) bludgeoning damage, and the target is Grappled (escape DC 14). Until this grapple ends, the creature is Restrained, the target takes 7 bludgeoning damage at the start of each of its turns, and the Biter can't constrict another target.

Frightful Screech (2/Day). As a reaction to taking 10 or more damage in a single attack, the Biter screeches, forcing all creatures within 10 feet of it to make a DC 13 Wisdom saving throw or be Frightened until the end of their next turn.