Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) piercing damage. If the tembril scores a critical hit against a Medium or smaller target and the damage reduces the target to below half its hp maximum, the target must succeed on a DC 15 Constitution saving throw or be instantly killed as its head is removed. A creature is immune to this effect if it is immune to piercing damage or doesn't have or need a head.