Here´s an easy way to make a ninja mask in 7 steps:
Step 1 - Pick a t-shirt of yours. Any will do.
Step 2 - Turn the shirt inside-out and put over your head normally but with the tag down (backwards) and hold the sleeves out to the sides.
Step 3 - Tie the sleeves in a single knot in the middle of your head. Very simple (pull
it tight so the mask does not become loose during battle.)
Step 4 - Frontwards it should look like this with the tag down under your nose.
Step 5 - Pull the top collar down your forehead and fold it up. Keep the facial space to a minimum and pull it right to your brow.
Step 6 - Pull the bottom collar and tag up over your nose and fold it under the same as you did with the top collar. You will find the sides, where the hand is on the mask (in picture), will fold into each other quite nicely.
Step 7 - Find yourself an interesting yet threatening ninja pose. You´re now ready to be a ninja.