“Since the vile Plante’s Deceased Hoste is not technically a Part of its Anatomy, any attemptes to Kill the Monster using regular methods is likely to prove Futile, especially that of Beheading the Creature. It seems to regarde its Head as a most Unnecessary part of its Composition, and thus as it moves its Head exhibits a frightening lacke of Expression, and lolls in a way most Unpleasant to observe.”
Long sieges can be a trial for both sides. For the beseiged especially, finite ammunition supplies always pose a problem - except when the ammunition can reproduce…
The PCs find a strange helmet, when donned it will take control of that PC and speak and act trough him/her. It explains that it is benevolent and needs their help in a quest and that it will stop possessing the PC when the task is done. Great if a player is gone for a number of sessions.