Stage1 - Shikaku: Divide the grid into rectangular or square pieces. Each piece must contain exactly one digit, that shows its area. Stage 2 - Star battle: Place stars into the grid, so that each shikaku rectangle/square has one, and each row/column/3x3 box contains two of them. Stars can't be adjacent, even diagonally. Stage 3 - Masyu: Stars from star battle act as masyu circles - if it has a digit in the same cell, it is black; if not - it's white. Draw the single non-branching non-intersecting loop. The loop should pass through all circles in such a way that: White circles must be passed through in a straight line, but the loop must turn in the previous and/or the next cell; Black circles must be turned upon and the loop must travel straight through the next and the previous cell. Stage 4 - Killer sudoku: Normal sudoku rules apply. Groups of cells not visited by the masyu loop act as killer cages. Those groups and killer cages already drawn in the grid must all sum to the same total.