I second Paper Mache.
My San mask and all of my Samus armor is constructed out of it,
. I too prefer accuracy, so I first make a wire framework (this allows you to shape and bend the form if alterations must be made) and then cover it in aluminum foil or duct-tape to flesh it out, and then place paper mache atop that. Protrusions can be added with Model Magic after the piece is mached.
Note: There may be some bumps, crinkles or divets, but if you fill and sand paperclay or layer enough of it it will become smooth. Also, I found that a 2 part Elmer's Glue and one part Water solution works best for the mache.
PS: I wanted to be Skull Kid long ago when the game first came out, lol, but never got around to making it. It's nice to see that people still love Majora's Mask!