Possessor of some sort (demonic of devilic)
Dc 18 will save or be possessed, repossesses whenever killed. – other than that, party doesn’t know stats.
The Yekatohu is a creature of frost and evil, of icy heart, soul, and body. Cunning and evasive, as well as thouroughly vile, it is notable for it’s ability to tear apart a party by possessing a member and using them to sow fear and paranoia among it’s members. It is notoriously hard to kill, with some theorizing that it is impossible to truly destroy, that it is only possible to imprison it through one of a variety of methods.
It was first encountered by the party of Red Hair, Panacea, Old Guy, and Quaralon, where it promptly possessed old guy and used it’s influence and the course of events to result in an explosion which killed in all but one of the members. It left this one member alive choosing to turn the thier fallen companions into undead to torrment the survior’s emotions. It now runs free through the northlands (presumably) wreaking havoc.