This is amongst one of my most interesting designs. Since there is already a toad and snake navis, I based Forestman's over all concept off a tree gecko. The tree on his back was inspired by Torterra (from Pokemon). Though, it seems kind of one dimensional with only one kind of tree on his back. I tried varying the trees, but it didn't turn out so good. As for the bird, it was a last minute addition.
Here's a bit about the character: Forestman is one amongst a "Special" group of Navis. He is a huge nature enthusiast and also has a calm demeanor. Despite having a calm, and friendly-like appearance, he's one of the strongest amongst the other "Special" Navis. He is the only Navi with more than 5 battle abilities. What's ironic about Forestman is that while being a major nature lover, he's almost always seen smoking; which we all know is obviously bad for the environment.