SU-3D-OKU!

It's Sudoku, but with an added dimension. Standard rules apply, every line and region must contain one of each number. However each line and region now goes through to the next layer as well, so don't think of each layer as its own puzzle. Instead think of all layers as a cube of which you are only viewing one slice at a time. So try to image what the cube looks like from a different angle when solving the puzzle.