Step 5: Adding details
There are two antlers which jut from the temples of this helmet, so the first step is to mark where one will come out (Pic 2). Use your blueprints as guides here to make sure this falls on the same place as the original in-game helmet - a set of bow calipers will really help with the symmetry as well. (Pic 3)
Once you've determined where these parts will be mounted, cut out a couple of recesses with a dremel tool and seal the underlying foam with more acrylic paint (Pic 4). This may seem specific to this helmet, but many other helmets from video games have crests/horns/pointy bits sticking out of them. Looking ahead to the mold making step, this would make molds and castings very difficult. The more modular you can make things, the better.
I wanted the antlers to bolt in from the sides of the helmet, so I vacuum formed small recessed blocks to serve as "plugs" for their mounting points. These were glued into place with epoxy. (Pics 5, 6)
The base of the helmet is another part that needed some additional shaping. Looking back at our blueprints, you can see the side profile has a gradual curve to it, and the underside of the helmet has a beveled edge. Adding an MDF or (as shown here) sintra block to the base will create this lip, which can then be shaped with a dremel tool to the proper bevel. (Pic 7)
In Pic 8 you can see a series of numbers placed along each inch of the lower lip. One half of the helmet was shaped first, then these numbers were added. By measuring the height at each number then transferring these measurements over to the opposite side, you can make sure that both sides of this complex shape are identical. (Pics 8, 9)
Add a bit more filler to blend these new additions into the rest of the helmet, and continue on to step 6!