I recommend buying the best wingman available and doing this challenge on the first Forest level "Strength in Numbers." If you have a good wingman, he'll do most of the work for you, but I recommend using the Silvertail dragon with the Lightning Vision skill. That skill is ideal for this level because most of the enemies are tiny ones, and just sweeping around the Lightning Vision takes care of them pretty well.
Using this strategy I was able to get the challenge after three very fast runs, and I never had to use my secondary skill until the very end. And even then you probably won't need it.