As the Party is traveling through the woods, to the party.
This does indeed sound like a trap, but I have a idea, that may just disrupt it, the only problem is if this Balion can travel through the trees and control trees, what is to stop him from spying on us using them.
I have a way around that of course, using that spell I mentioned earlier would prevent eavesdropping. I would can only use it on three of us however, and would need your permission. Afterwards we could safely strategize with ease.