As far as the loading message, I do not see that as much of a problem, but will probably remedy it later. Chat history, on the other hand, would be impossible; as every bit of UserInfo storage is used already. No place for history! Oh, and killing a link: select the user whose link you wish to kill and click on the 'Clear' button.

The world constuctor that starts with 'super' should have a 'prepare();' call in it. With that, this should run online. But, you could also include the enemy (Alligator) in the 'prepare' method.

You could also add constructors to 'stopper' and 'generator' to 'setImage(new GreenfootImage(1, 1));', so you will not see the green heel(s) at the top of the screen.