I made an alternate "transmuted weapon" version of the arm grill to be snapped onto the lower vinyl forearm piece in place of the regular grill, but I'll cover that later.
For the upper arm, I made an oblique cylinder of plastic which I decorated with studs. The cylinder was made large enough to slip over the bicep.
To create the elbow decoration, I deviated from the set pattern a little. I started by cutting long, banana-shaped sections of foam, covering them with plastic, and then hotgluing them to the lower end of the bicep piece, creating something which resembled a medieval elbow cop.
I cut out a shape like this to create the "upper bar" of the elbow decoration.
I glued a simple straight strip of foam and plastic to the front of the elbow piece, then glued circular pieces to both sides of the elbow and sank studs into them, as shown:
The elbow cop portion of the armor should, of course, be glued in such a way that it's resting directly over the elbow. With the bicep portion of the armor done, it was then time to move onto the body of the arm...
Next step: the body...