I know it isn't much, a bronze medal and 2 greens (also got 3 blues and 2 gems).

But it's better than nothing! Basically what I did was run in immediately, getting off the bridge ASAP. Then I just started running a circle around the fire elem, all while throwing spells sideways at him. I avoided circles on the ground, and managed to run 4 laps around him before I finally died. I wasn't up next to him, I was farther out sort of near the wall edges.

If you try this guy, do not stand still. Run in, do laps around and avoid the circles. If you stand in a circle or stop, you will die fast.