My party, Land druid, Shadowheart, Lae'zel and Gale, went to the tree where Kagha was to meet the dark druids. Both Gale and my Druid cast Flaming Spheres and commanded them to roll and frolic in the combustible twines that covered the area, burning up the Wood Woads since they were weak to fire, burning up the twines to stop them from being healed and before too long, both Wood Woads and all the Ancient Mephits were dead.
While all this was happening, my party was hiding by the edge of the water to avoid being set on fire by the rapidly spreading flames. By the time they were discovered by the Young Mephits, the party just mobbed them up with Magic Missiles from Gale and crossbow bolts from the rest.
So, how much cheese did I use? Just a slice of Kraft, or a gourmet cheese shop's worth?
Would your DM allow it? How would he make the enemies act to prevent the fight from being so one-sided?
This is a really good use of Flaming Sphere, It's not cheesy at all. As a DM, I like to reward creativity. I would roll perception checks for the Wood Woads and Mephits, versus the party's stealth check once they started burning.
Depending on how difficult of a fight it may have been intended to be, I might consider adding another wave of Wood Woads and Mephits to come into combat.