“ A casual remark by one of the party about something met on a previous adventure leads to a summons to and grilling by the Mages' Guild (or equivalent), probably resulting in an expedition back to that area to recover the things for study by the Guild. The party's presence will be 'requested' for this expedition.”
“ A massive iron key - 2' length, 20 lbs forged with demonic faces from the bones and horns of demon-lords. When used with a massive portal - carefully built according to documents found in powerful books of evil knowledge, it will open into the realm of demons and allow them to flood into the world. The applications of this item for villains are obvious. Mortals touching this item are subject to [Effects_of_Touching_Powerful_Evil_Artifacts]”
“ 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.”