1 Step Forward, 20 Years Back
A Tale of Two Stans AU:
Instead of fighting over the journal Stan tries to leave, but Ford isn't willing to let him go that easily. During the argument Stan comes into contact with a strange magical substance, and when he wakes up later he finds he's a bit smaller than he remembers.
Now not only does Ford have to worry about Bill taking over the world, he also has to figure out how to turn his brother back to normal.