I love the monochromatic cave our hero falls in at the end of the demo!
You need to take more inspiration from Super Mario Bros. II (U.S. version) instead of Super Mario World.
Or, if you stick with Super Mario World, please make it a distorted, surreal version of SMW (an alternate universe, if you will. Or a psychedelic trip.)
Needless to say: great demo
Here's a few animated sprites in JB to show off in the mean time...
I like the character designs and animation. If the game features frogs, I suppose you probably have bats as well? Bats.