Illegal Position Analysis/Puzzles

What are some of the best chess problems that are based on illegal positions? I have seen a couple that involve dozens of bishops and other "grotesque" chess problems where the piece count is insane but the forced mate is still interesting to analyze. In the illegal position contest thread, the goal is to create positions that are very challenging to determine why they are illegal, but what are some positions/puzzles that are obviously illegal but still extremely interesting to analyze? Note by illegal I only mean the starting position is impossible, standard chess rules still apply.

Here's an example with dozens of dark squared bishops.

Another bishops puzzle. Anyone else have puzzles based on illegal starting positions that are interesting to analyze?

M4, white to move. Black has 4 queens, 4 bishops, 4 rooks, 4 knights, and 10 pawns.
Any other moves will result in M1 for black.

Here's what might be the maximum amount of material that a single pawn can beat, with a puzzle element to it:

The puzzle aspect is that white has to play 1.h3 to time the knight arrival at b3 when the queen is on a1, since a knight cannot triangulate or lose a move.

Nope - Just constructed this.

As for a single pawn:

That's two pawns though! The puzzle I posted starts with only 1 pawn! I can improve yours anyway:

There isn't any interesting puzzle aspect to it, just a checkmate position. Like my underpromotion thread, I prefer problems with a unique solution with a sequence of moves that has a puzzle element to it and is the only way to get a draw instead of a loss, or a win instead of a draw or loss.

That's why #7 exists. That's a rook though, it has to be a promotion to a rook. But yes, that's more material. I chose what I did because it was one of the only illegal positions i could think of.

In this position black can delay checkmate for 205 moves with the rook, by continuously sacrificing itself with check, until white gets to a position where he can avoid checks or capture the rook without stalemate. Now the piece count is far from being illegal here, but I wonder if an illegal amount of white pieces could be added in such a way that it extends the puzzle to 300, 500, or even 1,000+ moves! This is the type of "illegal position puzzles" I am interested in here. How complex could puzzles and studies get allowing more pieces?

Thank you my friend for displaying my illegal puzzle, however only the starting position is illegal not the solution. Please conceal the solution with a puzzle-form.

Yes I specified in the OP that by illegal I only mean the piece count in the starting position.

It's not illegal stuff based on chess rules, it's just the starting position is impossible due to the mere number of pieces. 50-60 piece positions are still interesting to analyze and potentially discover hundreds of move force mates due to the extra pieces!

Black is winning by -10 to -12 according to analysis.

An interesting challenge is to make illegal positions like that as equal as possible? How many more white pieces would make it more equal, which pieces and where?

My analysis won't show anything :/

You have to wait a little for the analysis to work, there's a huge lag when it comes to positions with 30+ Pieces, but it does work.