A single-solution helpmate which should provide entertaining solving.
1.Qg3 Qh1
2.Qg7+ hxg7
3.gxh1B g8Q
4.Bhb7 Qg1
Clearly the only way to mate is along the diagonal with a bishop blocking b7. Without the pawn at g2 Bh1 followed by Qg2 Qa8 Bb7 would work, but rather surprisingly both queens must be sacrificed.