Hoof Hearted

In my 'Inventory' some Armour items have a small, half filled, white diamond shape in the box to the right of the Armour pictogram. What is its significance?

I'm currently in Emerald Vale, back on the ship, having just installed the voltage regulator thingy. Can the autobot opponents on Emerald Vale regenerate? I'm looking for more to shoot at, to get the 'Short Circuit' trophy. Come to think of it, if I can I'd like to get some "TTD groin shots" in as well.

I helped Reed, for what it's worth. Then I shot him so I could get his access card and enter his sideroom.