Beast of caerbannog

False appearance. this creature is indistinguishable from a Harmless rabbit

standing leap. the creature can long jum p up tp 20ft. and its high jump is up tp 10tf, without a running start.

legendary resistance(can only use 3 times a day) if the beast fails a saving throw, it can choose to succeed instead

VORPAL BITE. Melee Weapon Attack: +6 to hit, reach 6 ft., 1 target. Hit: 4 (2d4 ) [piercing] damage. 

The monster can take 3 legendary actions, choosing from below. Only one legendary action can be used at a time and only at the end of a creatures turn. the monster regains spent legendary actions at the start of its turn.

Venomous Vorpal Bite. (cost one action) the killer rabbit of Caerbannog makes a single  vorpal bite attack dealing an extra 2 d4 of poison damage 

Vicious streak a mile wide. (costs 2 actions) the monster can move up to its speed without provoking opportunity attacks.