Discovered Checks in Chess
A discovered check is a discovered attack where the revealed attack is a check. Because the check must be dealt with immediately, the moving piece is essentially "free", it can go anywhere, capture anything, or even deliver a second check (double check).
Why they're so dangerous
The opponent MUST deal with the check, but the moving piece is immune. It can capture the queen, attack the rook, or set up a mating net. The most famous discovered check pattern is the windmill, a repeated discovered check that strips material.
Setting up discovered checks
Place a long-range piece (bishop, rook, queen) behind a piece on the same line as the enemy king. Then move the front piece with a threat, the discovered check handles the king while your piece devastates the board.
Training
Solve discovered check puzzles, they're among the most satisfying tactics to find.