Celestial Servant

Rather than being a normal animal or beast, your companion or familiar hails from the heavenly realms.

Prerequisite: Aasimar, animal companion, familiar, or mount class feature.

Benefit: Your animal companion, familiar, or mount gains the celestial template and becomes a magical beast, though you may still treat it as an animal when using Handle Animal, wild empathy, or any other spells or class abilities that specifically affect animals.

Source: Advanced Race Guide