Man, I can't tell if Eligion being able to stand and talk while missing his spine and a portion of his lungs is an indicator that something else is happening, or if it's just a very healthy dose of artistic license with anatomy.
Yeah, that eye and patterning. That scythe is either an earlier form of Puppet Sword or a related weapon. It could be that someone found it in the dungeon and it managed to possess or influence them to hide it until it was outside. The scythe might have planned this breakout and resurrection with the Demon King before the Hero's Party got there.
Whatever the case, it's probably going to take several resets before Kiska's able to get a handle on what's happening and what to do.