User blog comment:Mf99k/618 and Gravity Falls/@comment-3404455-20131213203117

6 Main Characters (Dipper, Mabel, Stan, Soos, Wendy, Waddles)

6 Fingers on the Journal (1, 2 & 3 and maybe?)

6 Books? Coincidence?

6 + 6 + 6 = 18

618!!!!