+1 stealth, and any minion that attempts to block this action and fails becomes tapped when the action is resolved (before resolving the action).
Clarifications and Rulings
Faceless Night taps the (successful) blocker when the block is successful, as normal. (If the blocking minion wouldn't normally tap when he blocks, Faceless Night will still tap him.) If the acting minion uses a Change of Target, then the tapping effect of Faceless Night is undone by the Change of Target. [LSJ 19990526]