Bandersnatch

Bounding Charge. The bandersnatch is unaffected by
difficult terrain.

Frumious. The bandersnatch seethes with barely repressed rage and anger. If it misses with its bite attack or falls below half of its hit points, it succumbs to such uncontrollable fury that it bursts into eerily colored flame. While engulfed in these flames, a bandersnatch is affected as by a haste spell (this effect can’t be dispelled) and deals an additional 7 2d6 fire damage with each of its attacks. The fury lasts for 5 rounds, after which the bandersnatch can’t enter a fury again for another 5 rounds.

Gaze. A bandersnatch can direct its gaze attack against a single foe within 30 feet as a bonus action. That creature must make a DC 20 Constitution saving throw, becoming [Tooltip Not Found]  (as per the confusion spell) for 1 minute on a failure, or restrained for 1 round on a success. A creature confused by this ability can make a new saving throw at the end of each of its turns to end the effect early.

Hard to Kill (1/Day). Through sheer force of will, a bandersnatch revives itself from a violent death. When reduced to 0 hit points, the bandersnatch is returned to life with 1 hit point at the start of its next turn, unless it was killed by a critical hit.

Magic Resistance. The bandersnatch has advantage on saving throws against spells and other magical effects. 

Planar Acclimation. The bandersnatch always treats the plane it is currently on as its native plane.

Quick Recovery. A debilitated frumious bandersnatch recovers with frightening speed. If a bandersnatch starts its turn affected by any or all of the following conditions, these conditions end at the end of its turn: confused, any levels of exhaustion, poisoned, and stunned.

Relentless Tracker. A Bandersnatch can move at up to double its speed and still track without penalty. It gains advantage on Wisdom (Survival) checks made to track creatures it has wounded.

Tail Quills. The bandersnatch has twenty-four tail spikes. Used spikes regrow when the bandersnatch finishes a long rest.
A creature attempting to remove a lodged quill must use an action to perform DC 20 Wisdom (Medicine) check. On a failed check, the quill is still removed but the process causes 11 (2d10) piercing damage to the victim. On a success, the quill is safely removed. If the check succeeds by 5 or more, an additional quill can be removed.

Vicious Tenacity. If damage reduces the bandersnatch to 0 hit points, it must make a Constitution saving throw equal to the damage taken, unless the damage is from a critical hit. On a success, the bandersnatch drops to 1 hit point instead.

Multiattack. The bandersnatch makes three attacks: two with its claws, and one with either its bite or its tail slap.

Bite. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 21 (2d10+10) piercing damage, and the target is grappled  (escape DC 20). Until this grapple ends, the target is restrained, and the bandersnatch cannot use its bite on another target.

Claw. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 19 (2d8+10) slashing damage.

Quills. Ranged Weapon Attack: +16 to hit, range 300 ft., up to four creatures that can be no more than 30 ft. apart. Hit: 27 (6d8) piercing damage and the creature is poisoned until the quill is removed.

Tail Slap. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 28 (4d8+10) piercing damage and the creature must succeed a DC 20 Dexterity saving throw or have a quill lodged in its flesh, and is poisoned until the quill is removed.

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.

Move. The bandersnatch moves a distance equal to its full movement without provoking opportunity attacks.

Claw. The bandersnatch makes a claw attack.

Tail Slap (Costs 2 Actions). The bandersnatch makes a tail slap attack.