Once, one of your pawns (any file) may step one square diagonally forward onto an empty square. Not a capture. The step must angle toward the center files.
You draft Drawbridge in Buff mode. Passive: it works on its own the whole time you hold it, with nothing to activate.
As a movement card, it changes how one of your pieces is allowed to move.
“Lowered once, toward the middle of things.”