It took me way too long to decide what to draw for this challenge, so I ended up with very little time to work on the actual drawing and consequently it isn't my best work. It was fun, though! I think Fred and George and Merry and Pippin would definitely stage a fight between Treebeard and the Whomping Willow if they had the chance :P
Here's a link to a speedpaint of this drawing, to prove that I did, in fact, draw it: https://www.youtube.com/watch?v=y73omnusXP0