OK. Now I understand. 2…Rd5 3 Nd3!! Rxd3 4 Kc2 and now the well-known 4…Rd4! threatening to sac the Rook for stalemate after 5 c8=Q, but 5 c8=R!! Ra4 6 Kb3! and either mate or loss of Rook. So there are two different underpromotion variations to two different pieces.
Nicely solved & explained!
When passed pawns are involved, the king vs. rook dance happens more often than one might think in “real life.” Sometimes the rook does OK.
L. Kubbel, Bohemia 1908
White to play and draw