Lego Man Costume - Halloween Costume Contest via /costumeworks/. 2 cardboard boxes for the head and body, glossy spray paint, and disposable paper bowls on the body and head. Paint on the face and cut out the mouth.
Lego Mask Free Printable - Two Sizes - Lego party con Imprimibles (Lego Party Printables) - This site needs translation, but still usable. I also like the mini Lego bags that can be used as belt loops.