Barbed Hide. At the start of each of its turns, the snake child deals 20 (4d10) piercing damage to any creature grappling it.

Tail Spike Regrowth. The snake child has twenty-four tail spikes. Used spikes regrow when the snake child finishes a long rest.

Siege Monster. The snake child deals double damage to objects and structures.

Multiattack. The snake child makes two attacks, one with its bite and one with either its tail spike, or constrict. If it is grappling a creature, it can replace its bite attack with its swallow attack. 

Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 22 (3d8 + 9) piercing damage, and the target must make a DC 19 Constitution saving throw, taking 42 (12d6) poison damage on a failed save, or half as much damage on a successful one.

Constrict. Melee Weapon Attack: +17 to hit, reach 30 ft., one target. Hit: 20 (3d6 + 10) bludgeoning damage, and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained.

Swallow. The snake child makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the bite's damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the snake child, and it takes 21 (6d6) acid damage at the start of each of the snake child's turns.

If the snake child takes 30 damage or more on a single turn from a creature inside it, the snake child must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the snake child. If the snake child dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

Tail Spike. Ranged Weapon Attack: +7 to hit, range 100/200 ft., one target. Hit: 18 (4d8 + 2) piercing damage.