Originally Posted by pr0xyt0xin
I think the Power Gem would work. Being that Ultron's eyes/mouth/energy are classically Red in color.
And that the Power Gem "augments the users physical attributes, such as strength and durability, to near infinite levels, and with mastery can allow the user to mimic the effects of energy based superpowers."
which makes sense considering adamantium isn't an option.
And, "It can also be use as an unlimited power supply for any machine."
which just screams Ultron.
well, considering Ultron's face may change... -_-.