SunnyShineUp has this prototype Fire Guts Optimus Prime on eBay.
Energon Mode - Instead of attacking with 2 different figures, you may attack with Optimus Prime twice.
So if he is your last figure, you no loner suffer from the loss of an attack. AND if he has the "Last Man Standing" Special, this guy will be a beast!
Thanks to greyelephant for his keen eyesight!