I know you said that graphics and sound aren't yours... but you choose them, and give game this aesthetics, so, I will give high score to visuals, because... game got it. (sorry, it's not about author, it's about game ~_^)
Whole prototype are really neat, environment trolling player (boat, bridge... hey, it's troll bridge, good one :D), i like that grow/shrink magic. Ability took both mushroom and magic stick would be cool, as same as ability to jump without necessity drop everything. It leads to a lot of backtracking, which is kinda boring (I understand, in small demo like this it's not crucial, and you got more play time this way ~_^).
Overally... I wanna see more of this game ^_^