A term for this game that is an extra battle occurs either by chance or just an extra. There is an option to fight the Invade boss (Left button:Fight!, Right:Flee). Failing to defeat it will result in all accumulated items, Coins, and exp. The option before deciding to fight or flight indicates the possible items that you can get from defeating the boss. They often contain rare items and Servants. The redder the header on the boss gets, the more dangerous (this is because it is based on level differences between you and the Invade).