Thing took the bottom off the mask (5)
I believe the answer is:
matte
But I can't explain it at all! Could you help me understand?
(Other definitions for matte that I've seen before include "Mask used to block out areas of the image in filming" , "Mask used to record two images on same film" , "A dull finish" , "Dull, flat" , "Mask used to add an image in front of camera" .)