This is Digiko, dressd up as Garrus from the Mass Effect series. I had to drop his name in there because if I hadn't told you, you may have thought this was simply Garrus from the Mass Effect series.
Taking around two months to build and costing $US300 in materials, the Mantis sniper rifle is based on a Nerf Recon, and it's built mostly from EVA foam.
If you're thinking the eyes could do with some work, he says that's because they're not "blacked out", which they will be for conventions, etc. If you've ever seen an effects man, or an actor in an animal suit with "panda eyes", that's what he means; it helps create a seamless transition between the suit's eyesockets and the actor's actual eyeballs.