I saw there was only two themes on gravity falls, a Dipper one and a Mabel one. I felt good old Bill Cipher needs some love!
Image is from the gravity falls wiki
The image does not belong to me, it was featured in one frame at the end of the intro in season 1...
Though i did not make it myself i'd prefer if you did not take it and said you made it since well thats kind of not true but whatever.