Ok, so let's start showing the build log for this one!
The raw cast looked like this:
After removing the visor area, teeth holes and cleaning up the neck, it was time to start in on the carving for this build. I used a Dremel with a couple different sized engraving bits. For cracks... PLAN them out. You cannot put it back once you carve it out, without having to fill and sand. So, use a pencil and plan it. Carve about 1/16" to 1/8" based on your material. You want it to look substantial without actually weakening your helmet. The weathering will sell it. In my mind, the brow ring and mohawk are separate pieces so the cracks do not continue onto them (they go under).
Now on this build the thing I get asked about the most is the blaster mark. I decided to do this off the cuff and made up as I went... Another case of plan your move in pencil. Think about the direction the blaster bolt is coming from, and the direction of any shrapnel. This is a brave member of the 332nd who would be facing the enemy, so the bolt hit a glancing blow and spread back, wider. Don't go too crazy here, Start small and expand as needed. The paint and weathering will really sell this. I carved mostly around 1/16" deep, with a little variation. I used the same Dremel bit as the cracks. Be wary of a heavy hand here as too gouged will look fake (or faker than a sci-fi blaster bolt...).
All of this was done before an ounce of paint. Speaking of paint...