Bandersnatch

Frumious Fur Coat: The bandersnatch is covered in a cruel bristling coat of sword like spines coated with a powerful feyborn venom. When a creature hits the bandersnatch with a melee attack it must succeed at dexterity saving throw DC 19 or take 8 (2d6) piercing damage. A creature that takes this piercing damage must succeed on a subsequent constitution saving throw DC 18 or be sickened by the pain from the venom until the end of its next turn.

Wonderous Regeneration: At the start of each of the bandersnatch's turns it regains 20 hit points if its health is above 0. Damage from a vorpal weapon negates the regeneration. 

 Legendary Resistances 3/day. When the bandersnatch fails a saving throw, it may instead choose to succeed.

Multiattack. The bandersnatch makes four attacks: one with its bite, two with its claws, and one with its barbed tail 

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 22 (3d10 + 6) piercing damage.

Claws. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) slashing damage. 

Barbed Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 24 (3d10 + 6) piercing damage. A creature that takes this piercing damage must succeed on a subsequent constitution saving throw DC 18 or be sickened by the pain from the venom coating the bandersnatch's spines until the end of its next turn.

Chaotic Breath (Recharge 5–6). The bandersnatch exhales a line of radiant and necrotic energy that is 60 feet long and 5 feet wide. Each creature in that line must make a DC 19 Dexterity saving throw, taking 36 (6d10) radiant damage and 36 (6d10) necrotic damage on a failed save, or half as much damage on a successful one.

Swallow. The bandersnatch makes one bite attack against a Medium or smaller target. If the attack surpasses the targets AC by 5, the target is also swallowed. While swallowed, the target is blinded and restrained, it has total cover against attacks and other effects outside the bandersnatch, and it takes 21 (6d6) acid damage at the start of each of the bandersnatch's turns. A bandersnatch can have only one creature swallowed at a time.

If the bandersnatch takes 30 damage or more on a single turn from the swallowed creature, the bandersnatch must succeed on a DC 18 Constitution saving throw at the end of that turn or regurgitate the creature, which falls prone in a space within 10 feet of the bandersnatch. If the bandersnatch dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 15 feet of movement, exiting prone.

Burbling Rage: When the bandersnatch is reduced to less than half its health its roiling blood burbles to the surface, coating its skin in a flaming coat. While covered in this flame, the damage taken from a failed dexterity saving throw against the Frumious Fur Coat is increased by 8 (2d6) fire damage and all attacks gain 8 (2d6) fire damage. It is also effected as under the spell haste until its flame dies out. 

The bandersnatch can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The bandersnatch regains spent legendary actions at the start of its turn.

Bristling through the tulgey wood. The bandersnatch can move up to its speed unaffected by difficult terrain.

The vicious tail goes snicker-snack. The bandersnatch can make a barbed tail attack.

There's no galumphing back (Costs 2 Actions). The bandersnatch is a consummate hunter, and will never let its prey escape. It lets out a hauntingly beautiful cry and all creatures within 60ft. must make a wisdom saving throw DC 16 or be unable to move away from the bandersnatch until the end of their next turn.