Illegal Position Contest!

Here's #6430 with some pieces removed, still illegal.

I'm not going to be fooled. I always check my board orientation first!

EvinSung's position (the post above mine)

I tried this far but realised that there might not be sufficient moves for legal retractions.

>> Black needs to move the a-pawn to the b-file and then to the a-file to get to a4.

>> The light-squared Black bishop must exit from b6, but getting to e8 after the b6 exit door is opened will take a lot of moves. By this time, the a7 pawn must have gone to b5 and the b7 pawn must have gone to b6 already.

>> One of the last few moves would have to be g3+ Kh5, but getting the light-squared White bishop out to d1 will equally take many moves. By this time, almost the entire of Black's army will be paralysed.

>> Now, Black only has one move left (bxa4), but White needs several moves to get the f1 bishop to d1.

With all of the above in mind, I conclude that EvinSung's position is illegal.

See #6387.

one move behind

Here is a proof game for this supposedly illegal position.

A position with both sides in check is always illegal.

What piece(s) could be removed to make the position legal?

queen on a4

That's one of five piece removals that would make the position legal. What are the others?

If just the knight is removed, the position is still illegal.

The five removals that would make the position legal are:  Q, Q+B, Q+N, B+N, Q+B+N

knight is on b3

How did the pawn on h2 get to g3?

Illegal

Can removing one black pawn from the board make the position legal?

Yes, on g6

Is that the only one?