The pitborn is the result of demonic influence in a humanoid, and unlike the 5e version with THESE you slap on anything you want. Tails, claws, fangs, hooves, weird colors and patterns and horns, whatever! They have innate magic to create clouds of darkness, and the adept has learned magic for things like invisibility, magically charming, weakening, and restraining!
First it's important to understand that Bruce has Dissociative identity disorder, and every Hulk is just one of his altars given a physical form. New ones can emerge at any time, but these are the ones that tend to stick around.
Savage / child Hulk
He's the most common Hulk, and the one everybody's familiar with. Is basically a giant traumatized toddler.
Joe Fixit / Gray Hulk
Has the style and personality of a 1940s gangster.
Green Scar / Worldbreaker
A more mature version of savage who is basically Russell Crowe in Gladiator.
Devil Hulk
Finally we have arrived at the big daddy. No really he's dad. Is protective of Bruce to the point of extreme violence, is also very intelligent.
Non-alter Hulks :
The Professor / Merged Hulk
Merged Hulk was the integration of Bruce/Savage/Joe's personalities, which is the end goal for some DID treatments. In essence he is the whole package, Bruce with as much of his shit together as he's ever going to have.
Maestro
Evil tyrant merge Hulk, ergo, evil tyrant Bruce from an alternate Earth.
Revamp of my pitborn tiefling rogue, Malthus Ziel Drezdan
Your local teenage dirtbag. Favorite activity is to annoy his Abadar-follower father because of course he's too chaotic for this shit.
(yes it's the same drawing, I've just muted the caolor down because my computer is shit at rendering intensity and my boy was too pink)