A quick demo to show an idea to FishingPro98. See thread: http://scratch.mit.edu/discuss/topic/50601/ The crab is "moved around" with asdw - actually the background scrolls.... The fishes movement is completely random, which is a bit frustrating, but it's intended to demonstrate moving a sprite around off-screen and on-screen.
Use the Alternate Move block to control the Shark with arrow keys. This is a really rough demo. Feel free to remix, re-write, copy or ignore. I hope it will be helpful.