As I stated earlier, I made a Trol/Wizard/Vampire. But he was a mistake(he was a wizards apprentice who got caught in the middle of an unfortunate miscasting of a nasty summoning spell), he became a troll and a vampire, but retained his casting ability and his regen abilities, plus the strength of the troll. But being a magially created being, I just ignored the no con no regen thing. (it fit with the campagin/adventure) Also pointing out that as a GM you can create anything that is counter to the books, it may take some imagination to make it credible to the PC's, but it is possible. (After they killed him they found his diary, and found out he was a magically created entity, and was angry at humanity(read humans/elves/dwarves/hobbits...ect.) but that was a condition of whom his master was trying to summon(a powerful demon lord that hates humanity) and he found out that his "disease" was transfered to any creature that he bit(much like a vampire), but it also polied them into a troll. he was trying to make a race of them to attack the human lads)
Just my 2 cents
Just my 2 cents