The balloon is the method of seeing who is in the lead at any one time. The larger the balloon is, the worse you are performing. When the balloon gets too large (past its marked "Limit") it will explode and that team will lose. The balloon is inflated by being killed (+20%) and by getting struck whilst KO'ed (+1% or 2% per hit). You can adjust the Limit of the balloon at the start of a Versus Match.