Since everyone is so adamant that no one will guess the cliffhanger, I've come up with some crazy theories of my own. Prepare to lolz.

Shawn inherits a Candy factory and moves to Poland

A shape-shifting soldier from a parallel universe kills Gus and takes over his body (cue Fringe crossover)

Shawn and Lassiter find out they are related

Shawn and Juliet find out they are related *dies*

Santa Barbara is overtaken in a zombie apocalypse

The chief is pregnant…with Lassiter

Yang enters a radio sweepstakes to win two tickets to a monster truck rally and invites Shawn

Shawn finds out he’s adopted

Mary wins the racquetball world cup

Lassiter is Yin

Shawn’s mom is Yin!

Shawn finds various missing toys from his childhood in Yin’s apartment

Lassiter leaves the police force to catch his big break on American Idol

Shawn finds out he’s just been hijinxed kwa Henry (at least one of wewe must have seen that onyesha on Nick@Nite)

Mr. Yin is actually a toy poodle named Scruffy

Yang has been remote controlled kwa a man behind a curtain all along

Shawn gets hand-picked kwa CTU and Jack Bauer to help stop an assassination against the president

Shawn is forced to face his fear when Patrick Dempsey turns out to be Yin

Juliet receives a Hogwarts letter

Yin turns out to be none other than Alfred Hitchcock, himself

Yang gets chosen to be a contestant on Survivor: Antarctica

Lassiter decides to embrace his childhood kwa bidding on a Razor Scooter on EBay

Enjoy Mr. Yin! 13 days!