Lib
From Mario Fan Games Galaxy Wiki
Libary files for The Games Factory or Multimedia Fusion, consisting of sprites. In early ages, libs would be like a playable mini-game in which you could use the sprites if you wish. Over time, libs began to include more and more useless sprites, such as "pregnant Amy Rose". Later on, sprite-sheets were added and rules were made much more strict, limiting libs to only a specific type of sprite per lib and banning the silly mini-game aspect.