Open line for checkmate (2 moves)
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This is a very common checkmate combination, that often includes sacrificing material. You can think of the blocking piece being pinned to the checkmate square.
Black can open the line for the rook from a2 to h2 with the queen sacrifice Qh3+.
White is forced to capture the queen with gxh3, and Black can checkmate with Rh2#.
White can open the line for the pawn from e6 to e7 with the knight sacrifice Nf6+.
Black is forced to capture the knight with Bxf6, and White can deliver a discovered Boden's mate with e7#.
Black can open the line for the rook from f8 to f1 with the queen sacrifice Qxg2+.
White is forced to capture the queen with Rxg2. The rook is also deflected from protecting f1, and Black can checkmate with Rf1#.
A line can also be opened for the checkmate attack (instead of for the checkmate move).
It is also possible to open a line for a fork, or for a capture (use the pin).