Clone of Super Mario Bros. World 1.
This is absolutely cool how the physics work and all. But for when Mario gets hurt, I saw you used opacity. There is a behavior called Flash. Other than that, cool port!
I'm well aware of the flash behavior. I tend to avoid several of the built-in behaviors because of how little control you have over them. Usually the primary issue with these is the order of operations. You can't control when the behavior runs, so you can't make sure certain things happen before or after it. If the behavior is so simple that it can be replicated with only a couple of events, then it isn't worth the potential headaches that can result from using it.