The Scarab of the Celestial Cog is a small mechanical Scarab that enters into the skin from contact to a humanoid "deemed" worthy, it then starts to burrow its way to the chosen creatures spine where it then latches onto and starts transforming the creature into a mechanical form of them selves,(that being said it does not turn them into a machine, it is more like if you were born a robot, you still have your genetic code its just made of metal.), This processes can be slow or long depending on if the character resists, Resisting the transformation requires a constitution saving throw with a DC of 20 or higher, on a success you can cut it out of your body with no ill effects, but if left in you would have to continue to roll a constitution saving throw. On a failed roll the player will take a 1D10 worth of damage and the scarab will start the transformation and will no longer be able to resist the transformation. If the player does not resist they can avoid the saving throw and and immediately start the transformation. When the transformation begins it will start turning the creature by killing them as there entire body is being turned into bio-metal they will continue to look and think the same. All weapons will fuse into there body and become part of them(if they have a bow it becomes a mounted cross bow attachment, if they have a sword it can come out of there arms, get creative), there base armor class will rise to 15, but they will no longer benefit from any armor, they will have a dis advantage on stealth rolls and are heavily damaged by elemental magic(excluding fire) They become resistant to slashing and piercing damage and gain in advantage on how any mechanical checks(being knowing who invented it or how it is made/works). They also gain a scarab familiar whit can be made at the expense to there own health 1D6 worth of damage(this scarab DOES NOT have the same effects as The Scarab of the Celestial Cog it is just a Scarab Familiar).    

Notes: Resistance: Slashing, Resistance: Piercing, Disadvantage: Stealth, Attunement is achieved merely by accepting the transformation