Carrion Brood mother

Keen Smell. The Brood Mother has advantage on Wisdom (Perception) checks that rely on smell.

Spider Climb. The Brood mother can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Multiattack. The Brood Mother makes two attacks: one with its tentacles and one with its bite.

Tentacles. Melee Weapon Attack: +8 to hit, reach 10 ft., one creature. Hit: 18 (3d8 + 4)poison damage, and the target must succeed on a DC 16 Constitution saving throw or be Poisoned for 1 minute. Until this poison ends, the target is paralyzed The target can repeat the saving throw at the end of each of its turns, ending the poison on itself on a success.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit:  12 (2d8 + 4) piercing damage.

Poison Cloud: when hit by a ranged attack the carrion crawler emits a noxious cloud. Creatures within 10ft of the Brood mother must succeed on a DC 15 Constitution saving throw or take 16 (3d6+4) poison damage.

Burrow: When hit by a melee attack on a d6 roll of 4-6 the Brood Mother Burrows under the attacker emerging in an unoccupied space with 60ft,this moment does not provoke an opportunity attack and can only be performed twice per day

Venom Spray (recharge 4-6). at 3/4 hit points the carrion crawler can spray a poisonous mucous from its gullet in a 15ft Cone once per round as an additional attack. Creatures in the affected area must make a DC 15 Dexterity saving throw and take (2d12+4) poison damage on a failed save or half damage on a successful one.
Creatures that fail the save have disadvantage on all attacks until the end of the Brood mothers next turn.

Frenzy. at 1/2 hit points the Brood Mother goes into a Frenzy it's movement speed is increased to 60ft.
it's multi attack increases to 3; one tentacle attack and two bite attacks.
And it now takes half damage from all non magical Bludgeoning,Piercing and slashing.

Swallow. At 1/4 hit points the Brood Mother goes berserk and attempts to swallow a random creature and escape. The Brood Mother makes one bite attack against a Medium or smaller target Within range. If the attack hits, the target is swallowed.
While swallowed, the target is blinded and restrained it takes 10 (2d6+4) acid damage at the start of each of the Brood Mother's turns. The Brood Mother can have only one creature swallowed at a time.

If the Brood Mother  takes damage, the Brood Mother must succeed on a DC 15 (or half the damage which ever is Higher) Constitution saving throw at the end of that turn or regurgitate the creature, which falls Prone in a space within 10 feet of the Brood Mother. If the Brood Mother dies, the swallowed creature must be cut free or on a DC 15 strength save escape emerging prone.