The Objects of Power are all cursed and particularly detrimental to a character's sanity, particularly those with the Fault of Influence.
Jalan's Book (Monestary of Tuath, pg. 35)
Joderine's Dagger (Black Moon Handbook, pg. 54)
The Vulture's Mask (Black Moon Handbook, pg. 63)
You should have the NPCs make a check to see if the the Object influences their sanity and actions.
Using the official ones as reference we can assume:
- A Mental Resistance check at a particular frequency.
- The item should give a bonus equivalent to the side-effect.
My suggested chart:
Item Bonus | Mental Resistance Check | Frequency
+1, Complicated (14), Weekly
+2, Difficult (17), Monthly
+3, Very Difficult (20), Monthly to Yearly
+4, Exceptional (25), Yearly
Frequency could also be a trigger that causes the object to 'activate' and force the check, such as putting it on, being in a certain location, or even in the presence of certain events.
As for the drawbacks, they could be stat related, but I like the idea that they take over the character's mind, making him do things he wouldn't otherwise.
A
Lesser Object of Power could make someone engage in activities that go against their Conviction, gambling, drinking, having sex, or alternatively hoarding money, being less/more talkative (and the penalties associated with it). It is almost like a Crisis.
A
Greater Object of Power could make someone commit murder, steal, get into brawls that put their health or reputation in danger, or even making the character try to kill himself.