It works well up to 10 levels but not for 100.
I don't agree. One change may be helpfull:
First generate a MasterWorld. It contains the act methode with arrow-key-reaction and level-end-detection.
The LEVELWorlds than become subworlds.
This supworlds ONLY have the positioning of the objects to form the level difficulty and the images. Anywhere this code has to be and whats bad to have it in a separate class?
Besides I expact that this organisation makes it easy to write an level-generator for interested players.
Whats the better way to a 100-level-game?