Hardest Checkmate in 1

yess it is dxe6

tooo eassy dxe6!!!!

the only checkmate i see is in 2 moves, but that is my opinion.

Good puzzle

Qf6 is not Shah Mat

dxe6# e.p. but you have to know what was black's last move and it is considered an en passant delivering checkmate. 

Some math puzzles are tricky like this. For example.....you have a sphere with a 6" long cylinder cut out of it. What is the. volume  of the remaining material. 
The diameter is not given. However, the question is a clue. The question itself implies that the volume of the remaining material is not a function of the original diameter of the sphere. 

Similarly, perhaps the question here is the same kind of clue. The fact that it asks, "Where is mate in 1?" implies that there exists a mate in 1, and if the only way that can be is with en passant, then that might be a legitimate solution. 

Just sayin'.....

en passant is forced

Qf6+ Kxh6

You just defined the joke problem. Only in joke problems you are allowed to assume that a solution exists and use that as information to solve the problem - for instance by modifying the rules of chess or the rules of problem solving in a creative way. However, joke problems should always be announced as such!

Normally for chess puzzles, we adopt the necessary conventions. I understand from the retrospective approach that one can deduce that en passant had to be the move, but it's actually a little sad that we have to follow the convention.

Not really. The math problem I cited as an example is no joke. It's a real math problem and a pretty good one. I'll repeat it here:

You have a sphere with a 6" long cylinder cut out of it. What is the volume  of the remaining material?

The full solution requires the use of integral calculus, which is how I solved it. I learned later that there is a very clever, and much simpler way that requires only the knowledge of a basic calculus principle, and some simple geometry. 

It's not deduction, it's seduction. There is an infinity of problems and studies that can be made based on different assumptions of unknown information. For instance when it can only be solved when black starts. Or when there is an obvious solution with white castling and a hidden one without it. For the problem to be correct you must then assume castling is illegal or there would be 2 solutions. Or you play the move Nh5-g3 and claim a draw on the basis of the 50-move rule - simply because there is no other way to get the required draw without it. All the conventions exist precisely to forestall such weird constructions. Instead they offer you the conditions under which you may change the move, disable castling right or claim a 50-move draw - that is when you prove them thru retro-analysis!

No argument with that. I referred to the chess problem!

D5 pawn to e6 

I've also thought pf Qg6# but people are saying that you take with en passent en e6 correct me if i'm wrong

1. Qxg6+? Kxg6 or pawn captures.

If you are referring to 1. Qf6+, then 1...Kxh6 is possible.

Under the proper conventions of puzzle compositions, there is no mate in one, even though in the "improper" sense the en passant would work.

In any case, the position is illegal to begin with.