When searching for underpromotions in endgame tablebases, I sometimes come across a position in which both sides would engage in an underpromotion. These are very rare and just a curiosity. I'm not even sure that it's known. But I suppose it was to be expected that such positions would pop up in endgame tablebases.
The position below is a mate in 107 with perfect play from both sides. Far too hard for any human being. May be a draw under 50 move rule. I added the moves leading to both underpromotions.
