Here’s a puzzle I made quite a while back, I believe the type was on some Sudoku GP round. It’s more puzzle than sudoku. I’m not sure the “different digits” constraint is required to make this one unique, but it should help.
Rules Solve as a standard sudoku. In addition, subdivide the grid into rectangles, such that each rectangle contains exactly one shaded cell, and such that the number in that cell is equal to the area of the rectangle. Rectangles must not contain any digit more than once.
One of the non-standard puzzle types in the Serbian Grand Prix round is Shikaku with clues that are off by one (as “Shikaku Liars”). Here’s a practice puzzle.
Rules Split the grid into rectangles composed of grid cells, containing one clue each, such that the size of each rectangle is equal to the corresponding clue ±1. Or see the instruction booklet.
There’s another easier puzzle of this type on the Rätselportal: Knapp daneben – Rechtecke. Then, in the knapp daneben instance of the Hausigel Contest Series. The double-clue Shikakus on croco should also be good practice: 2014-03-01, 2014-04-04.