Hmm, I typed "difficult retro" on google. This was the first result:
I don't know how to set "illegal" positions in fen, so I will just write the pieces squares.

Pieces: Kc8, Kd6, Qc6, Rd8, Rf6, Ba8, Ne8, a7, b7

Colour the pieces. What was the last move?

I'm afraid it's too easy for you though, so I will look a bit further π

Originally posted by David113 Can somebody (SwissGambit? π) post some examples of difficult retros? but NOT PGs, please - I have enough of those.π

In essence, this stipulation asks you to find how a given (usually quite tangled) position can be reached legally. So that it really asks for a proof game but without insisting on giving all painful details of a proof game. You "only" have to find the tricky maneuver that is required to lock everything the way it appears in the diagram.

Originally posted by SwissGambit How did you find it given that the diagram was wrong?

I guess he googled "release the position", not the diagram, and found that in a "release the position" problem the position must be leagl so the 2 kings are a mistake.π

Originally posted by David113 I guess he googled "release the position", not the diagram, and found that in a "release the position" problem the position must be leagl so the 2 kings are a mistake.π