So I think all of this mecha stuff is going somewhere. Here's a WIP build of the O from Zeta Gundam, made of Heavy Gear, 40k, Battletech, and other parts. The head is from a Loud Ninja Games kit that has... issues.
Besides being heavily armored, surprisingly agile, and overpowered, the O carries a massively powerful gun and sports hidden sub-arms (between 2 and six, depending on the artwork). I thought to suggest the upper sub arms from the new artwork with omnimech legs with prominent joints, to show them folded into the shoulder armor.
As the campaign storyline is set on Mars, the ground-type O has huge tread movement units and boosters in armored housings instead of rear skirts. As I'm using Heavy Gear models instead of (ugh) standard mechs for the most part, this fellow has the characteristic V-Engine.