Puppet Master Hammer Mechanic

[Clayton Reed]

Hey guys I'm wanting some advice and ideas on a set up me and my GM are working on, we been enchanting a hammer up, and instead of a character permanently with it, we wanted a sort of puppet master mechanic, the hammer is going to be intelligent in it's own way, like a cursed object, when ever a person wields it, the hammer takes over them and that's who the Player will play as, curious if the community has any ideas for the mechanics of it, and what checks to do, draw backs, restrictings, and what ever else. Don't want it broken so of course there be a check on control. :)

[Name Violation]

Back in 3.5 i ran a campaign with the main villain like this. It was the Sword of Kas (3.5 intelligent artifact).

Look at the magus archtype bladebound for some ideas.

Basically you just make an intelligent item, and have it possess people.

[Name Violation]

The Sword of Kas is a +6 unholykeenvorpal longsword. It grants the wielder a +10 enhancement bonus to Strength. The sword is intelligent (Int 15, Wis 13, Cha 16, Ego 34) and chaotic evil. It can be used to cast the following spells, once per day each: call lightning (10d6 points of damage. Reflex DC 14 half), blasphemy, and unhallow. Once per week it can be used to slay living.
I also gave it telepathy 30 ft. Made for an awesome recurring villain, that can't just be killed off.

Is this hammer PC in a group of other PCs or just possessing a NPC?

[Name Violation]

Figure out the dedicated power and purpose of the hammer. The character holding the hammer gets a save when ever there is a conflict of interest. If they fail a will save the hammer is in charge until another conflict of interest. Then they can make a new save. Repeat as necessary. Getting rid of the hammer requires a save.