Each area has a certain number of Metroids Samus must defeat; when she does, an earthquake occurs and lava at the very bottom of the level recedes, leaving Samus free to move on to the next level and kill the next set of Metroids, ad nauseum. (crunkgames.com)
And a Bob - omb at the bottom of the level's end denotes a «2.» (techtimes.com)
This not only creates a more merit - based top tier, it creates drama at the bottom of each level, where desperate teams face must - win games to avoid relegation. (sbnation.com)