Cooper's Card/Briggs' Note Connection
This could be a gigantic leap, but doesn't the image that was on Evil Cooper's card (which also appeared on the piece of paper that Briggs left for Bobby, Hawk and Sheriff Truman) appear to look like a little like a bug? Perhaps, even the bug that crawled into the girl's mouth at the end of Episode 8?
A-ha. I'd seen the owl ring image before and made that connection, but didn't really notice what appears to be the horns (or whatever those two things are supposed to be) on "Mother."
I believe Doppelcoop's main goal is to find/contact the Mother/Experiment. For what reason is anybodies guess. My guess is that he wants to become or transform from Doppelcoop into a black lodge entity more similar to Mike and Bob.