Demon, Blood Fiend
'Vampire demon' sounds like a 15-year-olds deviantart oc, but apparently it's a D&D monster.
In further defiance of the idea that 'demon' is a consistent category, blood fiends are undead (12 HD) and seemingly lack the tanar'ri, evil, and chaotic subtypes. Their ability scores are pretty nice, with +16 strength, +4 dexterity, +6 intelligence, and +10 wisdom and charisma. Large size is nice, 40 ft. land and 80 ft. fly speeds are nothing to complain about.
Blood fiends have two natural claw attacks that apply negative levels, as well as a natural bite that drains blood (1d4 constitution). DR 15/good is useful, resistance 20 to acid/cold/fire is as well, fast healing 5 is great and turn resistance +6 has its occasional uses. 24 SR is a mixed bag, as always, but probably net positive.
Special abilities are about what you'd expect of a vampire. There's the standard-action Dominate Monster (very spammable), at-will Gaseous Form (mostly obsolete by now), Create Spawn (doesn't offer control, and only works on evil outsiders, so mostly irrelevant), and of course alternate form.
The latter is confusing. It allows the blood fiend to assume the form of a fiendish dire bat, fiendish dire wolf, howler, or nightmare, and also notes it gains 'the exceptional abilities of the form assumed'. Presumably, this is meant to say extraordinary abilities, which alternate form didn't grant back in 3.0, but if it refers to special attacks as a whole then the nightmare form makes this insanely broken. For the sake of reasonableness, I'll assume this just works as normal 3.5 alternate form (which grants extraordinary abilities anyway). It's still broken if Assume Supernatural Ability is on the table, but that's not the blood fiend's fault.
Finally, SLAs! At-will Detect Good, Detect Magic, and self-only Greater Teleport are all useful. 3/day Chaos Hammer, Darkness, and Unholy Blight are less notable. 1/day Blasphemy and Desecrate are okay. It's a bit disappointing how a monster supposed to hunt other evil outsiders has so many spells that flat-out don't work against those.
Anyway: I'm not sure what to think of this monster. 12 undead HD suck, but the chassis is quite good and the at-will dominate spam is amazing. The melee attacks are less useful but still relevant in a pinch, and the SLAs are niche but not useless.
I'm going to go with +0 LA as a starting point, tending towards +1. Do discuss!