Is this position legal?

Maybe, but more analyse IS needed in this case

What about white?

White's rook must have been captured at f6 by the g pawn. That's the only way for the DSB to come out. But for sacrificing white's rook, f1-f3-e3-e6-f6 is the route. But white's f pawn blocks the DSB from going out.

Still confused whether this is legal or not lol..

Great, this is the right thinking process. You try to solve, and encounter problems. Now all that's left is to try and find a way to bypass these problems. What could you try here? What options are you missing?

Illegal.

Yes. Black can, white cannot. :)

That's one of the answers. There also exists a way to allow white to castle instead of black - slightly trickier to find.

Can't find it. Too tough .o.O

That should make the answer easy. I had an answer with argumentation, but I should have copied it first before posting the comment. After posting the comment I noticed that I had to login again - or: all my text was lost and I could start over again.

It went something like this:

The black knight can only come at c8 from a7, b6, d6 and e7. A7 and e7 are impossible due to the pawns, d6 impossible because capturing the knight would have been the only way to answer the check. Therefor was the last move from the knight Nb6xc8. The b-pawn is now at b6, was not captured by the knight, hence had to be on b7 when the knight made his move. Therefor did the knight capture the LSB.

Black has a LSB. He can only have one after promotion. That means that the h-pawn of black is promoted to the LSB and has to promote on f1 or h1. All white pawns are still on the board. Hence must the h-pawn have slipped through the pawn structure - and here I made my mistake as proven by Frankwho.

First will it go to the g-file. Next to the f- or h-file. That can only happen by capturing twice. That implies that the h-pawn has caputered both pieces of white and that the capturing of the pieces is done from h6 to g5 and g4 to f3. The h-pawn walks then to the promotion line. Irrespective if the king moves to avoid check or not, but before the pawn is promoted has the king moved. Therefor is it in that situation impossible to castle.

#1300: the last move in this position was the move you questioned about in your problem prior to that.

This part is still wrong, and so the conclusion is wrong. You're still missing something about the pawns. It's a neat but common trick used here.

Also #1300 is illegal. It isn't just about the last move in this case.

[DELETED BY ME]

legal

I don't think the situation you told is possible. Can you show me a proof game? o.O

manouver the h-rook via h1 to f1-f3-e3-e6-f6 instead of your a-rook

Then how can the DSB go to a7?

f4 blocks the DSB's way.. Look carefully, I've tried that idea. It didn't work to me.

Sent by private message because I've already solved it in this thread once, and really other people should try solving it, it's a simple little trick that shows itself often in easier problems.

For those who want to try further, the white pawns are tricky.

Aah. I was thinking of trying that idea next because I don't see any other way. Nice one though!

I don't see how 1300 could pose any difficulty (what could Black retract?)

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