The problem is the case sensitive filenames. You've got to refer to the file in the code in exactly the same case that it is in the directory, in this case your mar.JPG needed to renamed mar.jpg. If you do that and re-upload, it should work fine. Incidentally, the new version of Greenfoot (1.5) will warn you about this, which should make this problem disappear from the gallery once people use the new version! java.lang.IllegalArgumentException: Filename 'mar.jpg' has the wrong case. It should be: 'mar.JPG' at greenfoot.util.GreenfootUtil.checkCase(GreenfootUtil.java:547) at greenfoot.util.GreenfootUtil.getURL(GreenfootUtil.java:515) at greenfoot.GreenfootImage.loadFile(GreenfootImage.java:170) at greenfoot.GreenfootImage.<init>(GreenfootImage.java:75) at greenfoot.World.setBackground(World.java:176) at Mar.iniciaJuego(Mar.java:245) at Iniciar.act(Iniciar.java:16) at greenfoot.core.Simulation.runOneLoop(Simulation.java:286) at greenfoot.core.Simulation.run(Simulation.java:157)

It seems quite jerky - was it smooth before? I can't remember, perhaps it's something I've just noticed but it does feel a lot better to me with smoother movement. Oh and making it smaller would still be good, vertically it needs to be about half the size it is at the moment to fit on my screen!

Brilliant! I coded a basic version of this a while back but never finished it and it was nowhere near this standard. Great work. It is a bit hard in the initial levels, but I guess that's just a preference thing - though personally I'd prefer it too easy to start with than too hard, but I'm just lazy ;) The other thing which I doubt is much to do with your code is that the game seems to crawl after a while, the garbage collector doesn't seem to picking all the garbage up so to speak. But overall, brilliant!

Nice start to this one! Few suggestions for improvement if you're looking to take this further: - The JOptionPane class is a nice one to use once in a while, but it feels slightly overused here! Perhaps build the character / world selection and the game over message into the world instead? - Animated characters are always good ;) - Rather than being able to walk anywhere on screen, would it not be better if you gave each world a different series of platforms, and then the characters had to jump between them whilst aiming and firing at the other? - Something to keep track of player's scores would be nice too :) - Networking? No, that's mean, ignore that one :P Good start though, keep going!