I have a serious suspicion one of the Adventure time writers likes Homestuck. No idea if this is old news or not, but:

Looks like


Possible coincidence, but still.

Probably a coincidence, but it could be referencing Dirk/Bro's Shades. Then again I guess it could just be an anime reference.

Nearly positive that's Jade that he drew on the board.

Blue muscular lumpy person with shades and a towel. Again maybe.