Every sticker on this cube has a lenticule coating allowing two different colors per piece. This makes it possible so almost every piece is present twice on the cube, but only one order of the pieces is correct because the viewing angle of a completed side should be the same for each piece. This means only the right pieces will share a viewing angle and lenticule orientation.
I solve this cube just like a 3x3, but I have to check the orientation of the grooves on the lenticule match all surrounding solved pieces as well as the appropriate viewing angle.
A solved Impossible cube being rotated to change the viewing angle