Hard Sudoku X
Hard Sudoku X — around 28 givens. By this tier the puzzle assumes you'll scan the diagonals every pass. Place a digit on a diagonal cell, and you've eliminated it from eight other cells at once.
Hard puzzles introduce locked candidates, pointing pairs, and box-row interactions. Expect 15–25 minutes per puzzle if you're comfortable with those techniques — and steady pencil-mark discipline.
Free downloadable Sudoku puzzles across four variants — Classic, Killer, Sudoku X, and Hyper — with answer keys on the back pages. No accounts, no colour ink.