Mate in 1

Someone to play and mate in 1!

The only checkmate I see is Nc4#, which isn't even checkmate.

You are correct in the fact that it is not checkmate. There is a hint if you need it.

Remove Black's Rc6 and Qc7.  Then dxc6 e.p. is mate.

Closer

Have you noticed that black and white have two kings each

Bxc5 doesn't work because of Rxc5. No, you do not need to checkmate all of the other kings. In this example it is 4-player (this is a hint). Think of what that means.

1.dxc6+  whatever  2.B(either) xc5 mate.

That's mate in 2

It's a 4 player game so both sides are theoretically making half a move each which makes it mate in 1.

Are there only 2 sets of colours on the board? Sorry if this question was stupid :(

Nice idea rookie. It wasn't what I had in mind but I suppose it works :)

It is meant to be one move (all up) though.

Rose, there are only two sets of colours in the sense that black can't mate black. However, some of the black pieces are one person's and some are the other person's.

Then it's just 1.Bxc5 mate and Black cannot capture with the c6 Rook because that is the other Black player's piece and it ain't his shot.

What's to say it isn't his turn next? Or that people with the same colour can't help when the other player is in check? Although if that were the case it would be correct.

I'm more looking for a mate that cannot be interfered with in any way.

White is going down the board, he's just played 1.e4 and Black replies 1...fxe3 en passant mate because Black's 2 Kings are in check from 2 different White Bishops and there ain't no escaping that!

Is there any significance of the fact that there are four players? Will the result be unchanged if its a 2 player game with 2 sets of kings and if any one king of either player is checkmated, the player is checkmated?

Yes, there is significance in the fact that there are 4 players. The result would be changed in a 2 player game with 2 kings each (I don't think it would be possible in a two player game). By the way, I got the original position wrong. I will fix it in a minute.

I solved it in my last post - it was a Helpmate.

No, unfortunately that was wrong. I had put up the wrong diagram. Sorry about the confusion.