You should fix some bugs...
Sometimes, if you run a level twice without making any alteration, the outcome is not the same.
Other times, when you make an alteration not related with another part of the level you've already built and tested, the tested part stops to work as it did.
 "Bloons Tower Defense 4"){kind=icon}
 "Creeper World Training Sim"){kind=icon}
 "Cargo Bridge: Xmas level pack"){kind=icon}
 "Cargo Bridge"){kind=icon}