Originally posted by XanthosNZ
Well let's have a stab at this.
The last move must have been black as white is in check. It must have been a pawn capture on f3. So the question is did it come from e4 or h4.
As the d, e and f pawns have not moved the g5 must be the h pawn as it cannot have reached there by any other means. That makes the f3 pawn the c pawn. Therefore it must have b ...[text shortened]... ht squared bishop is actually the promoted a pawn perhaps this is involved in what I'm missing.
The g5 pawn could also be the original g pawn and the g6 pawn could be the h pawn. I agree though, the last move had to be fxg3+ (which is what I assumend you meant). As for what piece or pawn it captured, I have no clue.
And as far as the Black's light-squared bishop goes, it had to be the result of the a pawn reaching the 8th rank... except, as you can see, a1 is a dark
square which means it had to promote at b1 via a capture. Now how it got past the bevy of pawns on the b file is beyond me, nor do I have a clue what piece it captured to advance to b1. I suspect that like the last "last move" puzzle in another thread, the bishop was placed there as a red herring. After all, it easily could have switched places with the d7 pawn and that would work as well.