The beloved of Bristlebane is the trickster's fondest creation, a 'bovoch'.
The spell itself takes about 9 seconds to cast, and yields a mix between a cow and a T-Rex, which acts like a self buff for you. This pet gives you a buff to AGI, INT, STR, WIS and STA, scaling to your level.
This pet is obtained by quest #5 in the Deity line for Bristlebane, Bristlebane's Beloved.