Something I introduced in my campaign recently that I thought might be worth sharing as we got some good situations out of it (thanks of course to HP Lovecraft):
The Lexicon Mortis is sentient book of Magic (Lawful/Evil) with it’s own objectives (relative to your campaign) and a human face capable of speech on the front cover.
The book allows the owner to cast any spell that appears in your own sourcebooks. However casting a spell requires a saving throw vs. magic. Failure means the owner becomes possessed by the book and will be their slave.
A suitably disturbing image of the book is here:
A simple concept - but one that doubled the drama when the PC’s found themselves in a very, very tight spot…