That's because of their association with Blue magic in MtG. But you don't need to be bound by art that is labelled that way, it's clear they could look like pretty much anything, from a normal member of the base species, to an anthropomorphic flying squirrel.I wish Simics could be any animal. I mean, I can always fluff them that way, but all the good Simic art is sea-creature based.
Yep, it only gets a short entry, but it is there, and simic hybrids would work fine for a PC who was an escaped experiment of Doctor Markov.I don't have the new Ravenloft book yet, but going by the TOC it looks like it's "Island of Doctor Moreau" domain Markovia, is still around.
I suspect Doctor Markov is still up to his old tricks, and probably would be the one behind creating such Hybrids in Ravenloft.