Vanish is a Prowess, this special kind of Feat can't be acquired until the third level. A Prowess is a special action that can only be done once per scenario. Unlike normal Feats, it can be acquired several times.
In the blink of an eye, the character is able to distract all of it's enemies and hide somewhere.
He may or may not be able to move from his position without being seen, but will remain unseen for a certain time if he doesn't move.