Not only is the way the scaling mechanic is implemented fun, it is also funny! It is unique and leads to all sorts of odd situations! Growing weapons or shrinking your enemy have intuitive effects. Also well done achieving this level of polish in four days! I didn't encounter any bugs.
Controls and objectives are both clearly conveyed from the start.
I think it's a little overpowered that I always get to see what the scaling effect is before I choose whether to apply it to myself or the enemy, but this isn't a detractor. I'm not sure how you'd change that without turning it completely into a game of chance.