Least believable part ...
takes place in Season 1, Episode 20. There is no way Dipper could have made that jump onto the giant Gideon robot. He had to jump almost the entire length of the bridge. I'm fine with the gnomes, zombies, and inter-dimensional stuff, but heaven forbid you have a 12 year old jumping the length of a football field.
Sorry, but I over analyze this stuff because my 6 year old watches this show constantly.