Tiny Magical Beast
Hit Dice: 1/4 d10 (2 hp)
Speed: 40 ft. (8 squares)
Armor Class: 16 (+4 Dex, +2 size), touch 16, flat-footed 12
Base Attack/Grapple: +0/-12
Attack: Bite +6 melee (1d6-4)
Full Attack: Bite +6 melee (1d6-4)
Space/Reach: 2½ ft./0 ft.
Special Attacks: Vorpal bite
Special Qualities: Darkvision 60 ft., low-light vision, oversized jaws
Saves: Fort +2, Ref +6, Will +0
Abilities: Str 3, Dex 18, Con 11, Int 2, Wis 10, Cha 4
Skills: Listen +7, Spot +7, Escape Artist +9, Jump + 4,
Feats: Alertness, Weapon Finesse
Organization: Solitary, pair or warren (7-16)
Challenge Rating: 1
Alignment: Usually neutral
Level Adjustment: --
The creature appears to be an ordinary white rabbit, although it is surrounded by bones and is flecked with the blood of a recently killed animal.
The legendary vorpal bunny is a predator posing as prey. Its bright coloration and harmless demeanor are how this vicious pack predator attracts unwitting prey. Pity the wolf who chases a "helpless" vorpal bunny into a field full of rabbit holes, which then explode with vorpal bunnies who had laid in wait.
Oversized Jaws (Ex): A vorpal bunny's powerful jaws are specially hinged and can open wider than they might appear to be able to, and do damage comparable to the bite of a medium-sized creature.
Vorpal Bite (Su): On a confirmed critical hit, a vorpal bunny rips the throat out of its prey, killing it instantly. Targets immune to critical hits are immune to this attack as well.
If you want to advance them, you could give them a Rake attack as well.