Not really a Magic Item but maybe a Wondrous or advanced mechanical

Not really a Magic Item but maybe a Wondrous or advanced mechanical 

(based on Randus Duthain, played by Brian Bergdall on the Critical Hit Podcast) 

Exilarchy of Cogs Battlefist 

A EoC Battlefist is a mechanical prosthetic made by the sentient Construct Race of the Cogs (or by some genius Artificer studiyng their technology). Actually supposed to be used as a swappable weapon for the Cogs warrior it can be reconfigured to connect to a living humanoid. Due to the intelligent design of the Exilarchy the Battlefist reconfigures itself to the needs of the user and can become much more then just a strong arm.

A EoC Battlefist has 2 Weight and is Clumsy

When you connect a EoC Battlefist to your living body, roll + CON as it analyses your bodily health and capabilities. 

On a 10+ choose 2, on a 7-9 choose 1 

* The EoC Battlefist looses the Clumsy Tag

* It configures a stronger outercasting, functioning like a shield. Take +1 armor 

* If your Class Damage is lower then 1d8 upgrade it 1 step

* It has room to imbed a small crossbow (1 weight, near, can only store 1 ammo) 

* It reconfigures the fingers to include different lockpicks, looking glasses and other thiefy tools

http://majorspoilers.com/wp-content/uploads/2012/06/Randus.jpg