I was wondering if anyone has seen or made a sudoku which gets HARDER as it is solved. Ideally such a puzzle would start really easy for a couple of cells, then each new value becomes progressively more difficult to solve, until finally the puzzle seizes-up (that is it becomes so difficult that it is near-impossible for a human to solve).

Best would be a sudoku with this property AND has symmetry.

Maybe such a sudoku would be a "backwards" sudoku (because more clues makes it harder), or maybe it is a "nightmare" because one might think they just need to get over the next hurdle, but really the hurdles get higher and higher (maximum frustration)!!