A player of mine is one of those guys who tries to put strange race/class combinations together, and altogether plays very gimmicky or OP characters. He can never seem to play "LG Human Fighter", if you know what I'm saying.
Anyway, his latest idea is this
Blood King - D&D Wiki .
Holy crap!!!
d12 hp, Fighter BAB, two good saves (Why not three on top of everything else?!), 6 skill points/level, class skills include just about every useful combat/adventuring skill not to mention stealth on what is ostensibly a fighter/arcane caster build (and why does a caster-based class need Use Magic Device?!), deliver touch spells through melee attacks, arcane casting without penalty in light armor, upgraded to medium if the character already overcomes the penalty in light armor, get both an evil version of the paladin's mount AND a familiar, and you get to be a vampire but with some of the limitations removed. And to top it all off, we get an epic level progression. Amusingly enough, there is absolutely no descriptive text whatsoever.
Yeah, it's a bit too powerful. No forget that, it's too freakin' powerful. I'm surprised there's no divine spells on it, or command undead, unless you removed it already.
As his DM, I don't want to tell him that he needs to just scrap it and come up with something less OP.
This is way way too powerful. You really do need to put your foot down because you obviously realize this is unbalanced and broken.
My recommendations:
HD: d6. Very little beyond dragons or barbarians should get d12 hp, IMO, and this isn't one of those things. Stream suggests d4, but you don't need to pull it down that far. It's a martial/arcane hybrid, so in between d4 and d10 is good. Eldritch knight goes d6, and that seems like a good match. Also, I can be a bit petty, so I'd deliberately lowball it to d6 simply because he had the gall to suggest something so overpowered. Like Stream said, he'll be upgraded to d12 at level 10, so he can look forward to it.
Cleric BAB. Again, martial/arcane hybrid, so take the BAB that averages the two.
I agree with Stream, good Will save only. He won't need Fort as undead. Really, when you come right down to it, the only thing undead really get to their favor is the d12 HD, because otherwise they have lousy saves, bonus to Will saves is kind of pointless when they're immune to mind-affecting stuff anyway.
Fighters get 2 skill points/level, wizards or sorcerers get 2 skill points/level. This guy should get 2 skill points/level, period. Really, 6 + Int/level is ridiculous. I wouldn't be surprised if he's planning to make this build with a wizard, in which case he'll get plenty of bonus skill points from Int (18 Int no doubt) already. Don't let him dump 3 or 4 more points per level on top of an overly generous 6. Then, trim the skill list. He does not need stealth, the class is not built on a stealth class, he probably wants to take full advantage of the vampire's +8 bonus to those skills. Ditto for Gather Information; there's no reason for this class to have it. Get rid of Decipher Script, he's got arcane spells, let him rely on
comprehend languages. Dump Swim from the list, vampires have an aversion to ruinning water. Finally dump Use Magic Device, as an arcane caster, he'll already be able use arcane scrolls and wands and such, don't give him the ability to use divine ones (possibly the reasoning behind this). Don't give him the ability to activate magic items evil creatures can't use without penalty.
Keep the spell advancement the way it is.
Dump the mount. That's just another unwarranted goody, particularly since he chose a black unicorn (*nitpick* and besides, only females can ride them yet he's using male pronouns for the PrC). He already has the undead familiar thing (which should be bumped up several levels), and since the class requires a base class that has familiars, he'll probably start with one.
Make sure that the character gets *ALL* the weaknesses of a vampire at level 10. So no crossing the running water, hates garlic, recoils from mirrors and holy symbols. There's also this interesting little line: "They are utterly unable to enter a home or other building unless invited in by someone with the authority to do so." you could rule that maybe he can't enter a dungeon and has to tool around outside. You don't even need to inform him of that beforehand; just make sure he understands he has ALL the vampire's weaknesses and let him come to the conclusion that you could creatively enforce the rules and not let him into dungeons under certain circumstances. Also dump that stuff about the cohort and coven going out of their way to make sure he resurrects, vampires are evil after all and do not need to be that loyal. That's just another too-good advantage, ensuring that his character gets rezzed, should he get killed, and rezzed without penalty no less.
Anyway, that should make a good start at bringing the PrC down to reasonable levels.
Or you could do it the easy way and simply forbid evil characters in the campaign.
This is on a wiki, so I am kind of tempted to...edit.

I don't really have the time to waste on it right now.