Near the end, Grunkle Stan accidentally drops his pen, notepad, and mug through a portal. These items can be seen coming out of one of Rick's portals in "Close Rick-Counters of the Rick Kind" on the show 'Rick and Morty,' which was co-created by Justin Roilland (Who also provides the voices for both of the title characters), who voices Blendin on 'Gravity Falls.'
A cartoon photo of Creator Alex Hirsch is pinned to Dipper's board of suspects for being the author of the journals, circled in red with "Who?" written over it.
"Blanching" is in fact a real word, meaning to whiten or to scald food.