Printable Sudokus (easy, medium and hard), solutions included: https://payhip.com/b/Ky4NH : r/sudoku
Sudoku - Samurai Sudoku
Sudoku Harakiri: 100 Hard to Extreme Puzzles by Kim Chi
Suicidal Sudoku Puzzle Book: 300 Hard Puzzles That Will Either Tempt You To Cheat Or Find The Suicide Forest In Japan And Perform Harakiri by Masaki Hoshiko