I am looking for some puzzles where there is a forced mate in as many moves as possible (ideally 20 or more). Yet the puzzles need to be as easy as possible!
You will probably need to find some puzzles where the defending side has a lot of spite checks to delay the mate.
I just made a very easy mate in approximately 23. White to move:
It's really really easy since Black can do nothing. But it doesn't totally satisfies me since the position is of course not legal...