... I think I'll be voting for Yunalesca. I am quite suspicious of a possible Taiga/Artsapat collusion, but I might be reading too much into that, and overall I think it's more likely that the only person not part of the gang is scum, than the only claimed non-human. From what little I've managed to read on the wiki, I know there is at least one major good guy who is also a vampire, and I'd be tempted to guess that's who we're dealing with, assuming Taiga is indeed not scum.

As for being such an obvious blunder that Yuna would surely have lied if she were actually scum, eh, we've seen worse. I thought the same thing multiple games back when only one person claimed to have been brought into the game in a burst of darkness rather than a burst of light, but in the end that person was indeed scum.

So yeah, I think this is our best bet.

Vote: Yunalesca.