Illegal Position Contest!

in this position, you missed it for a few seconds

I missed the same pentangulation you did, but at least you showed it was legal.

i did a heptangulation

you improved it to a pentangulation

And we both missed this one.

nope i found it

it was my sideline

i did it like this

That's right, I forgot again.

I have a memory like a sieve.

what?

also the king pentangulation can be done like this

there the order of king and knight dont matter

but i always default to nf3 ng1 so oops me in past

Obviously impossible, the dark-squared white bishop shouldn't be in the game

nope-

e4 d5 exd5 d6 d7 d8=b bg5 be3

another legal position in the lllegal position contest-

Ah, yes, obviously impossible.

Late again? Dammit! How do y'alls enter these games in so quickly?!!

you are faster in moves tho

Hahaha true!

I'm going to repost a position I posted over a month ago on the chance that AuroranMelody has not seen it. Those who remember the answer should refrain from giving it  away. What makes the following position illegal?

If the pawn on a4 was on a3 instead, would the position be legal?

What do you think?

Well, I tried to make a proof for it, to be honest. I'm thinking that in order for the setup in the top right corner to be made, the black king has to wait on g4, so the rook doesn't check him. But that means gxf3 hasn't been played yet. Once the setup is done, Black only has one piece that's free to move, and it has to be captured on f3 to let White's LSB out. After that, Black can only burn tempo by pushing pawns, and it comes up one move short before White can complete the position. The closest you can get is Black to move, with White's knight on h3, after which Black has to play a3 to pass the turn back to White.