For the logo, I used the pin prick method in the past. I printed up the size I wanted and then poked holes through the outline. I carefully put that on the side of the cake and ran my finger over the holes. When you remove the paper, the holes will be imprinted on the icing. Then you pretty much connect the dots to get the picture. Fill in the picture with the appropriate colors. Fortunately, I now have an edible image printer.
For the face mask, use gumpaste, or at least a 50/50 mix of gumpaste/fondant. Fondant by itself will soften when it is in contact with the buttercream. And if you can, do the mask a week in advance.
What I did was roll out ropes of gumpaste/fondant. I used a 1-1/2 gallon pitcher, covered with wax paper, that had an 8" diameter, so a hat box or some kind of cylinder with the same diameter would work. I rolled 2 pieces about 1 long each and another piece about 2 long. These form the center, vertical lines. (Follow the pics). I then took another rope and started about half way up one side of the pitcher, then looped it over to the same spot on the other side. Then lay 2 horizontal ropes. The ropes touched the countertop on both sides of the pitcher. There was probably a space of 1" to 1 -1/2" between them. I usually do this a week in advance to make sure it dries really well. The two ends of the horizontal ropes are the "posts" that are put into the cake. I believe the front part of the mask was just over 2" from top to bottom. If you have to paint it, don't forget to do the inside part of the mask, because that will be noticeable
You can do a smaller version if you want to, just use 2 - 6" layers for the bottom and one of the Wilton ball pans will fit. For the face mask I used a can the size of a large formula can.
These are very basic instructions. Ive seen some really good helmets with lots of details out there. But this will at least get you started.