Part Demon and part Vampire, the broxa is created at the whim of its demon parent/master. The percentages of demon essence and vampire blood combined vary depending on the creature's purpose, usually. Those created as slaves have enough essence to perform whatever task is intended, though not normally any more. A minimum of 10% is necessary for any broxa or it wouldn't fare well in Hell on a long-term basis.
A broxa is never created with more than 60% essence. Powerful enough to start having designs on its maker doesn't last long in the paranoid power schemes of the realm. It can also be taxing on a demon to pull enough essence to create something that essence-heavy.
Broxa cannot change form in the way a demon can. They are limited to changing age and all that entails (size, voice, strength), and may be crafted physically in additional ways, such as wings or horns, extra limbs, etc. Regeneration is based on its percentage; the more essence, the faster it heals and the less effort needs to be put forth to do so. It feeds as either parent does, not limited to one or the other. The more vampire blood in the creation, the more 'character' of the vampire is in the broxa. One made with a high dose of Toreador blood, for example, would have the distractibility and craving for beauty that the vampire donor did, as well as the vampire's abilities.
Credit
Credit for information goes to Spook.