Try looking into the Centimani in Promethean. They are not vampires, but they have some pretty cool ability to transform themselves using Flux. A Centimani would also have the ability to turn corpses into Pandorans, which can be all sorts of weird and inhuman. One of the creep factors I felt about the Tzimisce and their fleshcrafting was their ability to do it to other things. I haven't found that with the new vampire alternatives.
Of course if they're looking to play a Tzimisce rather than have them as villains... this may not be the best route.
From Mortal Remains p20
Within the already small subset of beings called Prometheans is an even less numerous category — the Centimani. These
so-called Freaks revel in their inhuman appearances and attitude,
and reshape their bodies in terrifying ways. Many have additional
body parts — a second set of arms jutting out from the rib cage,
an eyeball in the center of a palm, a face sprouting from the belly
or back. Centimani can sometimes change shape, turning into a
puddle of mobile blood or a horrific, canine-esque monster.
Other Prometheans seem to fear these creatures. They do not
follow the Pilgrimage — they have no regard for human beings and
have no desire to become one. They often travel with broods of
monsters, hideous, misshapen things that feed on the flesh of other
Prometheans. What, if anything, the Centimani have in common
with each other, and what their overriding goals are remain a mystery to the compacts and conspiracies. Whatever the truth, these
monsters are the Created without even the veneer of humanity. This
makes them easier to identify, but by no means easier to kill.
The best resource on them will be Pandora's Book