In the end I just decided to clear an achievement for getting the highest score on the leaderboard. This meant getting above 8000 on a single life. By warping to level four, I found I could stand in a corridor and kill all the enemies spawning around a corner; after a while the walls changed to exits and I could kill even more in the level. Not the most fun thing ever, though.
Gauntlet: generally boring
In the end I just decided to clear an achievement for getting the highest score on the leaderboard. This meant getting above 8000 on a single life. By warping to level four, I found I could stand in a corridor and kill all the enemies spawning around a corner; after a while the walls changed to exits and I could kill even more in the level. Not the most fun thing ever, though.