Hardened metal. Spectacular crystal.Engineering and arcana combined to create the perfect soldier, with no substitute or replacement. Your Strength, Dexterity, and Constitution are increased dramatically. Your Charisma suffers because of how alien you are. Even modern Warforged look upon you with apprehension.

You do not take Ability score increases as you level up. Enchanted items can affect your ability scores and behave normally.

Hit die Change: Basic hit die for Prototypes are 1d10 plus constitution modifier. Overrides Class hit die.

Armor Class Change: 17 + Dexterity modifier and shield AC (if equipped). Prototypes do not wear armor. (As always, DM's can decide if armor can be bolted on due to the Prototypes construction.)

Disease claimed more lives than any weapon ever did. Poison a close second. Eliminating these threats to a soldier was paramount in design. Composed of metal, gems, and arcana crystal, the Prototypes could wade through any battlefield without worry of being afflicted by any debilitating illnesses.

You were designed to fit multiple roles on the battlefield. Your limbs and torso can accept custom made, exotic, weapons. From arcane flamethrowers, shields with embedded blades, launchers of arcana and explosives, it truly was up to the inventor of what could be fitted.

Prototype characters do not have death saving throws, but that doesn't mean they don't have a chance if the unfortunate happens. The Prototypes were given an edge over death. One last chance to live and escape to fight another day. The design for a Prototypes helmet is just as important as any weapon created and used for the body. It is their life vessel. Upon the Prototype's health reaching 0, the head is forcefully ejected from the body (Choose a point within a 10ft radius for the head to be ejected to) and behaves as its own player-controlled creature. The head-vessel has a defensive weapon, set attributes, and a low health pool. Engage in combat at your own risk.

Attributes for the Head
Strength: -10
Dexterity: -10
Constitution: -10
Intelligence: Remains the same
Wisdom: Remains the Same
Charisma: -1
Hit die: 1d4 per character level with no constitution bonus
AC: 10 + Dex mod
Movement Speed: 40ft

Defensive Weapon - Arcane Beam:
1d8 Force damage
Uses Intelligence mod for chance to hit. 
Range: 15ft/30ft

After combat is over, the head can return to its body. Upon reintegration, the body gains a quarter of its hit points back and the Prototype's character assumes its full attributes. It regains another quarter of its health per long rest or can be taken either to a Forge Cleric or Artificer (or what DM designates as an equivalent) and repaired for the equivalent of its hit points that are lost.