How about portraits for when you talk to people? You may have already been doing that, but I wanted to suggest that just in case. That way you can give them more detailed expressions.
After Drake explains how powerful Bill is, Nicholas gets an idea. He gives the mind-ray back, so Drake didn't have to summon him.
Instead, Nicholas summons Bill and asks him to help by giving the humans a different outlook on the monsters of Gravity Falls. Of course, Bill takes advantage of this and takes over his body.
So, yeah... plot twist!
Remember how I was hinting that Drake was going to be the 'mysterious man' possessed by Bill? Really, I was planning on it to be Nicholas... *GASP*
Really! And there was a reason, too. After visiting the Mantuars and learning more about them, Nick decided he'd try and find a way to help them. Nick would find Drake and figure out he was trying to summon Bill... (cont)
If you need help with characters just ask me. I'd love to help! Developing characters and backstories just seems really fun to me, Like the one I had for our Gravity Falls RP. I never got to use it... >_<; Can I tell you?