Not great.
This isn't the worst game I've played, but it needs some serious improvements. First off, it's just a fight scene with three different difficulties; there's no story, no reason I should care whether I beat the boss or not. The player's hitbox is WAY too big; many times, the Frogon blew fire very far behind me, but my HPs dropped constantly while the fire was present. Also, giving the Insane boss an "instantly reduce player to 1 hp" skill is just stupid; how is the player supposed to survive, keeping in mind the ridiculous hitbox problem just mentioned?
Overall, the gameplay is stupid, as the best tactic is to go as far to the right as possible; this way, most attacks miss, and the ones that don't (which should miss) only take off a couple thousand HPs. However, this tactic makes all spells useless, which means the player is just sitting there at the edge of the screen, holding A, hoping that he doesn't die before the Frogon does.
Your sounds overlap one another, the animation is dreadful, the gameplay is terrible, it's impossible to jump, so why even bother to add platforms... honestly, you have the framework for a game, but you have a lot to build on it before it's an actual game.
Also, as a side note, I'm always willing to lend my services to help spellcheck or grammarcheck. Just send me a PM and I'd be happy to look over your script.