There is a popular type of scenario called Blood Fest. Units are automatically created until your tower is destroyed, at which point you lose the game. In my edition there are eight players. Players 1-4 are on one island, and Players 5-8 are on another. Once all but one player/team is destroyed on an island, the path opens to the other island. The champions of each island shall clash for supremacy once all opponents have been vanquished.