So I tried making a lvl 2 Wildblooded Sylvan Sorcerer with the boon companion feat.
The Sylvan Sorcerer archetype gives you an animal companion at LVL -3 min 1. The boon Companion feat increases that lvl by 4 max of your hit die. It should have been maxed, with a lvl 2 Sylvan Sorcerer having an animal companion as powerful as a druid of their level (3 HD).
It defaulted my animal companion to 2 HD. I know I can manually add a hit die but... it doesn't seem like it is working as intended.
I didn't check but it might have the same problem with the Mounted Fury Barbarian Archetype.
http://paizo.com/forums/dmtz2zgd?Ani...n-Companion#34