-two long pieces of ribbon
Tear (don't cut) a few sheets of newspaper into 1- to 2-inch thick strips. Tear out a piece of aluminum foil twice the size of your face. Fold it in half and press against your face, making sure to smooth it out as much as you can, getting as much of the detail of your face as possible. Lay a few sheets of newspaper beneath your workspace—this is a messy project—and crumple a few pieces of newspaper under your mold to help prop it up.
Make the paper mache paste. Mix 1 part flour to 2 parts water to get a runny liquid. Completely submerge the strips of newspaper into the paste and lay over your mold. Continue to do this, overlapping the sheets until the entire face is covered. Let dry completely (overnight) and apply a second layer. Do this at least three times. This is the most time consuming part of the process. After a couple of days, you'll have a mask perfectly molded to your face ready to be painted and made scary!
Make paper mache pulp. This pulp is what gives the mask it's shape. You can mold pretty much anything out of this stuff, it's so cool. Tear about three sheets of newspaper into little tiny pieces. Boil some water in a large pan and throw the newspaper bits into it. Stir until the pieces disintegrate, about 20 minutes. Add a little salt to prevent mold.
Pour the mixture through a strainer to remove excess water. Add a generous—and I do mean generous—amount of glue and mix together with your hands. It should feel almost like putty by the time you're done. I made horns, a nose, cheek bones and a goatee out of this. Because this stuff is mostly glue, you can pretty much just stick it to the mask and it'll hold, but just to be safe, add a little more glue to hold it in place securely. Mark and cut out small holes for your eyes. Wait a few minutes for the whole thing to dry (really, you should wait more like an hour, but I have no patience) and paint.
The paint is really the only thing you have to spend any money on. I bought an inexpensive set of six different color acrylic paints at an art supply store for under $4.
Punch out holes on either side of the mask and tie a piece of ribbon about a foot long to either side. Using fabric glue or Crazy glue, adhere the horns to another piece of ribbon that you can wear as a headband. You can wear this with just a simple red dress. I'll probably also wear a cape, and if I can get my hands on a pitchfork, that would be pretty sick. But honestly, the mask looks so good that it doesn't need much else.
Go out, scare the hell out of everybody and have a fun and happy Halloween!