Ploiatos was an original member of the crew, recently discovered to have been corrupted by the Ingress. Originally he was known as having appeared to the current crew and attacked them and Mana, the ship's navigation- [officer? He doesn't know if that's the right term. He leaves that there.] He couldn't be killed at the time, only contained, and it took several people leading him into an enclosed area. Somehow perception is directly tied to his capacity for mobility. If someone isn't looking at him he can act incredibly fast. If more than one person is focused on him, he can be cornered and herded.

At some point he managed to assert some sort of control over the ship, which is the reason for the current ill-effects on the vessel.