Blackburne’s Mate is a checkmate pattern involving two White Bishops and a Knight.
The pieces needed for this mating pattern is two bishops and a knight. This checkmate occurs when the opponent is castled and only one pawn is left of the three in front of the King and Rook. In this case, the remaining pawn would be in front of the Rook.
With a Knight covering the square in front of the empty square next to the King, a Bishop would be covering the empty square next to the King and the other Bishop moving to the opposite colored square that the Knight is covering, putting the King is checkmate.
Since it can’t move to the square your other Bishop is covering and can’t take the Bishop that put it in Checkmate because your Knight covers it.
In this example, it’s Black’s move but White is threatening mate in one. Black moves the Knight to attack White but it’s already too late.