Good vision. Darkvision 500 ft. Truesight 250 ft. (carrots are good for your eyes).

Keen Sense. The Rabid Rabbit is completely omniscient. 

Addiction. Rabid Rabbits have an intense love for carrots. If a Rabid Rabbit is within 5 feet of a carrot, it has advantage on all attack rolls, ability checks, and saving throws.

Fast reaction. If this is the first turn of a newly spawned Rabid Rabbit, it has advantage on attacks on all creatures, on any ability check, and on any saving throw, until the start of its next turn. Until its next turn, it can cast counterspell at will.

Legendary Resistance (3/Day). If Rabid Rabbit fails a saving throw, it can choose to succeed instead.

Spellcasting. The Rabid Rabbit is a 19th level spellcaster. Its spellcasting ability is DEX. (spell save DC 16, +8 to hit with spell attacks). The Rabid Rabbit has following Wizard spells prepared:

1st level at will: Distort Value, Grease, Jump
8th level (3 slots): Maddening Darkness

Multiattack. the rabbit rabbit takes 7 attacks in the following order: 3 with its claws, 3 with its teeth, 1 with its Carrot. 

Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 3 (1d4 +1) slashing damage. 

Bite. Unarmed strike: +12 to hit, reach 0 ft., 1 target. Hit: 4 (1d6+1) piercing damage.

Carrot. Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 62 (2d8 + 12 piercing), (2d8 + 10 radiant), (1d8 + 8 poison), (1d8 + 6 necrotic). The creature is now Blinded, Deafened, Frightened, Grappled, Incapacitated, Paralyzed, Petrified, Poisoned, Prone, Restrained, Stunned, and Unconscious. When attacked, the creature gains a sudden desire to become a carrot and will do everything in their power to become one. This fixation can only be removed with the wish spell.

Bonus Actions: The Rabid Rabbit may use one of each bonus action, after it attacks. 

Multiply. The Rabid Rabbit spawns in 1d4 more Rabid Rabbits in an unoccupied area no larger than 3 ft. from it. 

Divide. The Rabid Rabbit splits into 2d4 of the nearest creature's worst nightmare. That creature is then Blinded, Deafened, Frightened, Incapacitated, Prone, and Stunned. The affected creature's conditions last until the end of its next turn. The Rabid Rabbit reverts to its original form at the start of its next turn.

Hide. The Rabid Rabbit instantly buries in any direction a distance of up to 30,000 ft. This movement does not provoke opportunity attacks.

Cruel jest. In response to an enemy's verbal or psychological insult, flip a coin. If heads, the Rabid Rabbit heals to full health. If tails, the world ends.

Rabid Rabbit can take 10 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Rabbid Rabbit regains spent legendary actions at the start of its turn.

Munch. The Rabid Rabbit makes one attack with carrot.

Cluster. (Costs 3 actions). If there is a group of 5 Rabid Rabbits in a circle 10 ft. in diameter, the Rabid Rabbits may collectively take a legendary action and choose to cluster into a ball. The ball grows hot and flames shoot out. Each non-Rabbit creature within a 15 ft. radius sphere must make a DC 22 con saving throw or take 55 (10d10) fire damage, or half on a successful save. In order to use this action, each Rabid Rabbit in the cluster must have at least three legendary actions to spend.

Lunchtime (Costs 9 Actions). Carrots rain down from the sky. Each creature in a 300 ft. diameter centered on a point within 5000 ft. must make a constitution saving throw or take 155 piercing damage (14 d4 + 120) on a failed save, or half as much on a successful one. The Rabid Rabbit may choose up to 200 creatures that automatically save.

Rabbit Feast (costs 10 actions). Three creatures of the Rabid Rabbit's choosing receive something most unfortunate. 2d4 Rabid Rabbits spawn inside each of them and gnaw their way out. Each affected creature takes 85 piercing damage (21 d6 + 11).