So I envision a map with an island and a long bridge, with another island north of the long bridge where there are 5 gates that spawn baddies. The player or players begin on the Southern Island, and the baddies spawn and then immediately begin moving south , all baddies would be aggressive to the player and if players wait at the southern island there would be a long train of baddies with no where to run, best would be to run as north as possible and try to fight back the mobs before retreating until you are eventually overrun, the event would be timed so the longer you survive the more points you receive, or maybe the there is a time leaderboard.