Illegal Position Contest!

I have done some tests that make me fairly confident that it is illegal, but I could be wrong, just like how EvinSung proved my previous position was legal.

Try to construct a proof game, and see if it is possible; then you will know.

I think you're safe with this one. After three retractions, Black has no retraction to undo the check by the a4 bishop.

Blathy's creation is legal, even in the full setting with the knight on e1. We are sure though that at least one promotion has taken place. On which square?

rc4 to b4

updated 7622

there is also f3xg4

I had just realized I overlooked a retraction and made a proof game, but you've already posted one. I'll show mine, since it's shorter.

Oh I didn't think of that..white could promote one of the edge pawns to something which could then provide a capture.

RRRRRRight! (that is to say only one promotion square is certain) If I were to write down the hints for retrograde solving, that trick would be in the top 3!

You can uncapture a rook or knight on black's first retraction move which makes it (narrowly) legal.

In position #7636, black's rook starting on h8 was clearly captured by a white piece on its starting square or on g8, because black's dark-squared bishop was never able to get off its starting square with pawns still on g7 and e7.

True and we already "rectified the count" (bridge term) for that! The hard issues are on other places.

I was a bit confused on this version but it's still legal in the same way as the last one. However white needs to unpromote a piece on b8 to allow the black uncaptures.

please show a game if its legal position

I've messed up pretty badly on my previous position, but I know that this one is definitely illegal:

I feel like this is an extremely illegal position.

My feeling is that it is slightly illegal rather than extremely illegal, since the proof of illegality is extremely simple.

Bonus question: Could this position arise in a game of bughouse?