This was a giveaway at Toys'R'Us March 2015. The image I have found suggests me these masks don't have a have a set number. Here you can also see how instructions looks like. These are not your standard LEGO instructions you can find in sets or with other promos. The lack of set number and the appearance of the booklet with instructions suggest me you cannot get PDF instructions from LEGO Service for this set of bricks.
Keeping in mind this is just a bunch of 1 x 1 bricks on top of the plate, there shouldn't be much of an issue replicating the rest of the masks.