The fire vampire is a new vampire introduced in SLASH'EM. It uses the fire attack which is a deferred feature in vanilla NetHack, a counterpart to the Angel's magic missile attack and Asmodeus' cold attack.
The fire vampire can be very dangerous to the unprepared. It is very fast, with a speed of 24. Like all vampires, it has two claw attacks and a bite attack. It also has a touch that drains magic energy, and the ability to cast a spell that will cause you to be 'enveloped by flames!'. This attack can do upwards to 60+ damage without fire resistance. Note that at a distance they will zap fireballs at you. These cannot be reflected, and can still damage items in your inventory even if you have fire resistance. Fire vampires are best avoided until you have fire resistance; in particular, they make the Chaotic Quest a place to avoid for those without it.
Fire vampires are not actually undead, and thus are not immune to drain life, as proper vampires are.
Once you have fire resistance, these monsters constitute a very good reason to turn off the 'sparkle' option. They will usually get 3 fire attacks per turn, all of which will go through the sparkle animation, which can be quite distracting.
As a Polymorphed Form
If you have polymorph control, a fire vampire is one of the best choices for self-polymorph, given their speed, regeneration, innate flying, extra damage, low armor class, and ability to wear all armor. The major downsides are that the fire attack will sometimes destroy scrolls and potions in monsters' inventory, the danger of using an unintentional extra attack against stoning monsters (should not happen if you are wielding a weapon, but monks beware!), and the problems inherent to eating as a vampire.
A monster of the Cthulhu Mythos. Not created by Lovecraft.
It is not related to the usual undead vampires. Actually, it's two extraterrestrial monsters that share the same name. The flame Creatures of Cthugha that appear as many points of fiery light. And the fire Vampires of Fthaggua that appear as grimson bursts of lightning.
A swirling cloud of bright, burning motes, the fire vampire
descends upon its victim and easily burns them to death once
they are in its deadly embrace.