Great for a first!
It was a bit random and short, but it has great sfx and the bowser sprites looked customed, if so they were good. All i can suggest is making it longer with a more in depth story. Or make the fps higher so the animation is smoother, and make it as funny as you can. also i think the water should be from SMW, look at my "Fishy Water" flash to see what i meen. Allthough it's up to you, atleast make it seethrough so it looks more like water.