Queen attacks, bishop cuts the diagonal escape
A queen attacks the king while a bishop on a different diagonal cuts off the king's only flight square. The two pieces work like a crossbow (balestra), one piece holding the king, the other firing the killing line. Most often a queen-and-bishop pair with the bishop on a long diagonal aiming at the king's escape file.
Bishop to g6. Mate. The bishop covers f7 (the king's only escape) along the diagonal. The queen on d6 attacks e7 and covers d7 and d8, so the king cannot move there either. Both pieces are out of capture range.
Bishop out. Diagonal open, mischief possible.
3 more clean runs (at any point) to reach Recall.
White to move. Black king on e8. White's queen on d6 and bishop on c2 both eye the king's neighbourhood. The diagonal c2 to g6 leads straight to the king's flight square.
3 more clean runs (at any point) to reach Recall.