I've been on Pokemon Showdown lately, and if you give Shedinja a Focus Sash it doesn't faint, it remains alive until it gets hit again. Does this only apply to Showdown because I don't think this works in-game?
Since focus sash is only a one time use item*,Shedinja will faint if it gets hit a second time.
Source: Experience and testing.
*only for in-game, in wifi battles, the item will be given back to you after the battle