I'm having a lot of trouble with the new challenge arenas that were introduced with the PvP update in Magicka. I got the Final Frontier DLC and am trying to beat the Vulcan arena (though I'm assuming this question applies to all of the new arenas); however, I can only manage to get to the second or third wave each time.
I believe my problem is that against enemies in other challenge maps (and in adventure mode), it is a good strategy to play defensively. However, the enemies in the new challenge maps cast high powered spells very often, more frequently than I can defend against with shields.
Are there any good strategies for being successful in the new challenge arenas?