Pretty fun...
but I have a few notes. Firstly, it may have just been my experience but it seemed like the enemies had slightly better odds of getting high rolls. Second, if you are going to have multiple die then only counting the highest one seems like a waste, and leads to a lot of ties. Maybe the two highest, or the highest and lowest combined would make for a better system. The spells bothered me as well. I started out with time based magic, and it was annoying to watch my MP drain re-rolling dice when I already had a 6 on the board. Using the spells should be up to the players discretion. On a positive note, I liked the visuals and sound effects. Really, this seems like the bases of a battle system for a bigger flash RPG you might do in the future. Good job, hope to see more from you.