These anti-quads are so anti-everything that their antipathy needs to be spread out across four different cells to avoid overloading a digit. They might only list the digits they’re most against, but they don’t want any other digits doubling up, either.
Rules:
Normal Sudoku rules apply.
Digits within colored circles do not appear in cells touching the circle. The four cells touching a circle contain different digits.
Estimated difficulty: 1.5 out of 5
Solve on SudokuPad