Hardest mate in 1 puzzles

Indeed, it's a joke. See the posts after #6.

I'm pretty sure the Black to move thing was a mistake. As for the solution, you're right that the succeeding posts do include why there isn't really any solution.

However, I think the composer meant for the post to be taken seriously and isn't really a joke, since the composer kept insisting that en passant must be legal because it's the only mate in one... (which is weak, as Remellion stated a few posts later.)

why is everyone hating on this post and saying it's "easy"? you all must be GMs to be able to find out the solution

(on a serious note, how were there people who didn't work out that the post was satire?)

Not quite! The composer tried to trick us by omitting the coordinates. That was a willful act as coordinates are displayed by default. His intention was neither joke nor serious, it was evil

However by composition standards all problems with unknown deviations from the rules are formally classified as joke problems. There are quite a lot of those and very nice ones as well. But the consensus is that one should announce that a composition violates the rules by designating it as a joke problem without duty to tell you what the deviations are. That's where the guessing starts!

I solved the retro.

White's last move could be a lot of stuff. The 'answer' is that you promote your 8th pawn to anything (unless it is a light square, then you can't get a bishop) and then maneuver it to b2. the trickiest part is the black bishop. you need to make sure black wastes some time (when your pawn on h4) and then it should work.

It's a trick because black has to move and the rook could checkmate.

Nxc4#

Ahhh, of course!!! It never specified who had M1 and who had the move. It reminds me of a very famous composition by W.F von Holzhaulsen:

Mate in one for White

an illegal move must be made

You are looking at a different puzzle. This one is post #2 and not #6.

There is no illegal trick here. The composition rules (and this is a composition) prescribe that black moves first if it is illegal for white to move first as is the case in post #2.

Does anyone know why fxg5 is not correct as one of Black’s last moves?

Btw, there are more than 500 posts in this thread. Please specify the post number(s) your refer to since they are almost impossible to trace without this information!

Before you start asking questions you need to read and understand all the posts around the one you are quoting. As pointed out by Remellion (who has a fair understanding of retrograde analysis) the version in post #66 by Teddyhead (who is a total newbie on the subject) is still flawed. Therefore your question has no answer. Later Teddyhead posted a correct version in post #78. The answer to your question as it would apply to post #78 is that - if f6xg5 had been the last move - then it was impossible for all the pawns in the diagram to reach their destination squares from the game starting position without making more captures than material is available. To verify that may take you quite a while as pawn structure analysis is one of the core ingredients of retrograde-analysis and it takes time. If you do it right though you will be able to conclude that ..g7-g5 is indeed the only legal last move!

Addendum to previous post: The case against ..f6xg5 is actually very simple. Since there are 16 white units in the diagram, black could not have captured any white unit anywhere! In the post I formulated the general principle for investigating pawn structures and captures!

Easy

Rg7#

???

???

im late but, thats not mate in one.