I just had an epiphany:
There is only one possible explanation for Boris outing himself as the last Yellow wolf- he is in fact a Red Wolf (or at least a cultist/other baddie aligned with them).
It's very simple if you realize one thing:
Tonight is the Red's turn to hunt.
If Boris really is the last Yellow, he just surrendered the game. Even if we don't lynch him, the Reds eat him tonight. Even if the Red pack didn't believe his claim, they'd be fools not to go for the win.
Unless, of course, they are utterly certain that it's a ruse, because he is one of their own. In which case it's a clever move to protect Boris and smoke out goodies who fear losing the game.
As I see it, we must lynch Boris, because:
If we lynch him, and he's lying, we kill either a wolf, cultist or yet another innocent. 2 of three its a good thing for the good guys, and we've killed so many innocents what's one more at this point?
If we lynch him, and he's telling the truth, we lose the game on the same turn we would have anyway.
If he isn't lying, and we don't lynch him, and the reds eat him, we lose tonight
If we don't lynch him, and the wolves hunt anyone else, it's basically a confession. Yeah, they could be pulling a con on us to get the village to kill the last enemy pack member, but what does it gain them? It only delays their victory slightly.
As I see it, Boris is the one person left we can be 100% certain is not the last yellow wolf. Therefore, if you aren't a red wolf or their lackey, you should unvote Nautilu, Vote Boris!
To do anything else is to out yourself as a red-aligned baddie