These chess problems require you to understand the rules of chess. Assume White is on the bottom.
Expected difficulty Medium • Comment/E-mail if you want a solution to be published
Stipulation (12+13) White can still castle. Which unit made White’s last move? (Note that you’re not told whose move it is.)
Here’s one more. Apparently constructing chess compositions is harder than constructing logic puzzles…
Chaos at the Sky 
One quickly sees that the last white piece that moved is one already present on the board, which leaves a single possibility : ***.
Note that the stipulation could also have been something like “can white still castle ?”.
There are 2 black Rooks, but Rh8 can’t get out, so one of the Rooks is a promoted piece.
Because White still can castle, the promotion took place on g1, so the f- and g-pawn cross-captured.
BBc8 can be offered, the other offer must be a7 which promote first on b1. This can be S or Q.
It’s not important whose move it is, but the last White move is fxS/Qg3
bxc1=B is also possible, so fxBg3 is possible. But otherwise correct.