This week’s problem, with White mate in 5 moves, was composed by Darjan Marjanovic (Mat Plus 2009).
I’m sure you found the solution, involving two underpromotions.
1. c8B Kg1 2. Bh3 Kh1 3. a7 Kg1 4. a8R Kh1 5. Ra1#
Next time you reach an endings with seven extra pawns you’ll know exactly what to do!