"Dude, you crazy?! I've been waiting for you so long I grew roots and then I wanted to leave but I HAD to keep waiting! And I can't even knock myself on the forhead to express how stupid you are because my arm got stuck like that last time I tried to do it!"
When I painted his arm, I was thinking it just had only four fingers (cause you know, branches aren't limited to real anatomy ) and so that's the index finger, but it could be his middle finger if you like the idea better since I haven't defined how many fingers exactly the branch has, it's in the process of fusing and warping and stuff like that at the moment
When he's a tree all this bark stuff really acts as armor, you can't really hurt a tree with, say, an arrow. I imagine him uprooting himself and marching on his roots and the roots can dig through the ground and burst from under people and impale them or trip them or wrap around them so it's a terrible, terrible thing to run from. And in pointy-eared humanoid form he can probably pass through trees like a dryad. And ambush you... and maybe he can command vegetation to hinder your movement.
And a forest full of these guys and gals (probably they have female version too, just for the sake of equal opportunities (or some people's fetishes ), or those are actually real dryads)is a place you don't want to end up in unless you are a famous forest friend.