Here is a guide on Sellbot factories and promotions.
Promotions: To earn a promotion, you have to get MERITS. To earn them, first make sure your cog suit is complete. Then battle any Sellbot and you get merits if it is defeated. Here are promotions for cogs: (Note: If it’s hard to see just click on it.)
Factories: There are 2 factories(front and side). When you go in, be careful for goons(get caught in their light and you lose laff points), stompers, and cogs; lots and lots of cogs. Here is a map of the Sellbot Factories(thanks Toontown stratics):
At the end, you must battle the Factory Foreman(which is a skelecog).

