VS mode is a mode in which two players can fight eachother in any of the arenas. VS mode has no inpact on the quest itself, and battles conducted in the VS mode do not require you to go to +Centers if you loose HP. If you would like to use this mode, ask an overseer on the chat, and make sure your opponent has agreed to this mode first. You do not gain EXP from this mode, unless it is in a tournament.