Longo’s Absolutely Nasty Level 4 Feb. 26. 2013
KrazyDad SuperTough v5 #5 Mar 19, 2013
Paul Stephens from Weeks and Addicts May 28, 2013
Shortz Ferocious Beware! Very Challenging June 25, 2013
Shortz Trickiest Beware July 9, 2013
KrazyDad Insane v4 #5 2019 Update Oct 22, 2013
Pitkow Expert Jan 14, 2014
Pitkow GM Jan 21, 2014
Pitkow’s Super GMs Feb 11. 2014
Nikoli’s Sudoku X-tremes Sept 9, 2014
Wayne Gould’s Train Your Brain Su Doku Fiendish Nov 4, 2014
Antoine Alary’s More Extreme Feb 19, 2015
Gordon’s Mensa Guide Jan 15, 2015
Weekly Extreme June 9. 2015
Snyder’s Sadistic Sudoku July 28, 2015
Longo’s Nastiest Sudoku Ever Jan 19, 2016
Carol Vonderman Master Sudoku March 1, 2016
A.D. Ardson’s Very Hard v.2 July 4, 2017
Rebecca Bean Extremely Hard March 13, 2018
David Badger’s Hard Sudoku Aug 15, 2017
Manuel Castillo’s Only Hard Sudoku Sept 12, 2017
Castillo’s Only Extreme Sudoku Updated May 28, 2019
Moito Roadnto Mastery Jan 2, 2018
A. D. Ardson Sudoku Diabolical Feb 6 2018
World’s Hardest Sudoku Book June 26, 2018
Funster Extremes Sept 11. 2018
Shortz’s Hard Sudoku Beware I Dec 4, 2018
James Forest’s [Very Hard] Classic Sudoku April 30, 2019
Castillo’s Only Extreme Updated May 28, 2019
Lucky Panda [Extremely Hard] Sudoku July 16, 2019
F__ These Puzzles Are Hard Nov 5, 2019
David Challenger’s Super Fiendish Jan 7, 2020
J.B. Nakamoto Sudoku[Extreme Level] April 28, 2020
Puzzleproof Extreme May 20, 2020
Stefan Heine’s ultrahardcore Right Pages I Oct 20, 2020
Stefan Heine’s ultrahardcore Right Pages II Dec 29, 2020
Heine’s ultrahardcore Left Pages I Oct 19, 2021
Heine’s ultrahardcore Left Pages II Dec 21, 2021
Systematic Sudoku 