Sudoku Players' Forum (clone)

It is intended to be solved with pencil marks. I used JSudoku as a mark-up assistant.
Andrew has written walkthroughs on both of them at:

www.rcbroughton.co.uk/sudoku/forum/viewtopic.php?f=13&t=1691

On the assassin scale any killer puzzle from 1.0 upwards definitely requires pencil marks, maybe as low as 0.8.
In fact I use the interim stage paper solvable, so the solver is not to use mark-up assistants.
I do not consider either of these to be paper solvable.