Here is a Greenman mask you can download and make yourself. You need a printer, scissors and string.

Green Man Mask

Instructions: Download the mask here. Print the pdf. Card stock is a good choice.

Optional: To make a card that fits in a 5 x 7 envolope, fold along the two white marks, top and bottom of the mask. If folded the mask will fit in a 5 x 7 envelope. 

Cut out mask. The eyeholes may need to be larger depending on the size of your face. In the photo below Jim and I have very small eyeholes because we wear glasses. I had to enlarge my son's eyeholes quite a bit to accomodate his eyes.

The leaf on the bridge of the nose can be folded out.

Poke tiny holes where the two white dots are on the pdf - in line with the eye holes. A compass or sharp pencil will work.

Cut two pieces of string. Put a knot in one end, pass the unknotted end through the small hole, leaving the knot on the front. Elastic could also work.

That's my son and husband. I think we look like a gang of crooks.