The Hardest Endgame Puzzle?

I know some candidates though I would have to search for them. I guarantee you they are no fun whatsoever. You won't understand a single move of their solution and even engines can't solve them without our help to reduce the challenge. Worst of all it won't be possible to discern a single fun idea in their solution which is supposed to be the essential ingredient of puzzles.

The question is in the category associating with power. Which country has the most missiles? Who is the richest person you ever met? Did you ever attend a Madonna concert? The answers are irrelevant unless you are assigned a specific task but humans seem to believe the power shines on them when they know the answer. I have seen the most difficult endgame puzzle!! So what?

Btw, the best endgames are not the hardest ones but the most beautiful ones. They are often quite easy to solve because they play the paradoxical strings in our puzzle mind. I know for I made some of the hardest endgames in my day

Now I am used to operate in a short to medium-range of moves, 1-50 as the "real" long-movers are 3 digits, if not more. If they'll say sky is the limit, I'll say software is the sky & above. 

Addition:

But that is just the way I am seeing it, for the future of chess-compositions. I do not see how the generation used to cpu's and internet, would-go-make-puzzles the old-fashion, all organic and all by hand. I do not think they have got stomach for such adventures anymore. Unless a strange wood-dwelling hermit steps forward and proves me wrong, that is... 

some endgames require even more than 50 moves to win. Altough very rare, I suppose those endgames are close to impossible in difficulty, and in a real game you wouldnt have time to execute them before the 50-move rule!

More moves does not necessarily mean more difficult endgame. The pattern is the king!  

Bruh

:worry

Yes

More of an endgame study, but at 18 moves long it is a cool puzzle as well. Exact moves are required by the side with the knights, and other moves by the side with the king and pawn simply have the same result or speed up the process. I have no clue what the moves are for the next one but supposedly white has a forced checkmate in 96 moves here:

According to the tablebase LOL