A while ago this was the subject of a very long thread, where I posted an original example of a Win study with such a "promotion" key. You can see that position in my chess problem blog. At the end of that blog, there's a link to a forum where someone quotes a Mate-in-3 problem solved by such a key, and that's the only other example that I know of. There are a few other studies where promoting to a P is the only way to force a draw.
Examples of puzzle where only promoting a pawn to a pawn wins?
Sort:
Hey, I am looking for puzzles where the key is promoting a pawn to a pawn and any other promotion loses/draws. (I know that pawn to pawn promotion isn't legal today).