Here's a piece-drop puzzle of my own.
In the below position, a White piece is to be dropped onto the board. This means that, before White can move, they must legally put a single piece on them board.
However, there is a special requirement that must be fulfilled by the piece drop.
A single White piece has to be legally placed on the board such White can checkmate Black in precisely 12 moves. Additionally, there must be only one possible way to complete the checkmating sequence. Or, in a chess problemist's terms, it must be dual-free.
You must justify your choice of "droppage". by providing the mate in 12 sequence and explaining why it is a unique solution.
I accept any alternative answers that I have not thought of.
Have fun solving everyone!