What if this is how the anomalous otter makes more of itself?

Not a listed property of the stick, though there isn't anything to say that A!Ottter doesn't do something to the corpses...

Anomalous Otter may be another Mask that was possessed by the building. Or just turned mad. Considering Mask is the first one to enter a floor iirc, theres no telling how many Masks have been lost.

Yeah, Masks are the first to go. If they return, another of the team will join them for further exploration until the full team is deployed. If they return, that is.