MoP: Pet Racial Passive Abilities

The Pet Battles feature is still a work in progress and it has not been released on the MoP beta yet. However, there's more and more information being datamined about it with each beta patch.

Pets will not only have stats, levels, their very own special abilities (that are weak and strong against other specific pet types), but according to Wowhead News vanity pets will also be receiving racial passive abilities! [source]

Here's a list of each pet family type's passive ability so far.

• Critters -- Elusive: Critters break out of crowd control effects more quickly.
• Beasts -- Enrage: Beasts deal 25% extra damage below half health.
• Humanoid -- Recovery: Humanoids recover 2% of their maximum health every time they attack.
• Dragonkin -- Execute: Deals 50% additional damage to targets with less than 25% health.
• Flying -- Swiftness: Flying creatures gain 50% extra speed while above 50% health.
• Aquatic -- Purity: The duration of harmful damage over time effects is reduced on Aquatic pets.
• Elemental -- Weather Immune: Elementals ignore all weather effects.
• Undead -- Damned: Undead pets return to life for one round when killed.
• Magical -- Spellshield: Magic pets cannot be dealt more than 50% of their maximum health in one attack.
• Mechanical -- Failsafe: Comes back to life once per battle, returning to 25% health.

Remember that because this is still the beta testing phase, this list of racial passives might not be the final version.