what kind of animation du you mean? of course you can add animation, for example: -gifs (there is a gif support class on greenfoot support classes on this website) -create some pictures and let them swap in certain time stamps -you can change the transparency of pictures or scale them with the GreenfootImage class, try it and make your own animation out of images and scaling them or change their transparency for examples you can check out my game (as you already did^^) where i made all the animations by myself ;)

I like your idea :) maybe im just very attracted to space games :) Maybe you can try to optimize your hitbox? (try getOneIntersectingObject() or getObjectsInRange()) Or just try to make your pictures as big as the actual picture? Or just add some animations when hit? (explosion or something^^) Just some thoughts of me ;)