Southern Dungeons and Dragons - Rappan Athuk
Real name with only one Head is Cerb, second head is ur and the third is Us, combined they are known as Cerberus. Due to reasons, the party views him as a feline.
One day when they see a hellhound, they will truly understand. Despite this, Cerb is a loyal Eidolon to Oliver.
Feats: Power Attack, Weapon Focus (Bite), Improved Overrun.