How is the flying general rule used as an endgame weapon?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws for movement, checkmate and both repetition rulings: a side that forces a repetition by perpetual check or perpetual chase loses rather than drawing. The chase half has not been validated against the official casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it before publishing.
Direct answer
In sparse endgames your general controls the entire file it stands on: the enemy general may never step onto it with a clear line between them, nor capture anything on it if that would leave the two facing. That makes your general a free extra attacker. What the rule never does is give check: moving the last piece out from between the generals is simply an illegal move.
A free attacker in bare positions
Once most material is off the board, the general is often the piece doing the quiet work: it takes a whole file away from the enemy general, so your other pieces only have to cover the rest. The basic mates of a lone chariot, horse or soldier against a bare general all lean on it.
The defensive side of the same coin
A defending general has to watch its own file just as carefully: it cannot step onto the file the enemy general holds, and a piece standing alone between the two generals cannot leave that file. Knowing which of your moves the rule forbids is often what keeps a safe-looking position from collapsing.
Related questions
Does this count as a normal check like any other?
No. The facing position can never be reached, so it is never a check. A move that would create it is illegal and cannot be played.
Can this happen by accident?
Not on the board: the move that would leave the generals facing is refused. What happens by accident is a plan that relied on such a move turning out to be illegal, which is why clearing the central file in a simplified position needs care from both sides.
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