Double Fine posted a few weeks ago that https://www.trueachievements.com/Stacking-xbox-360.htm DLC was in development, but revealed nothing else about it. A couple of days ago, four new achievements appeared on Xbox.com for the game revealing its name and teasing very minor details.
Today, Double Fine have (finally!) announced what to expect of "The Lost Hobo King"! The downloadable adventure will hit the Marketplace in early April, bringing an all-new storyline in a brand new environment, heaps of new challenges and hi-jinks to discover, and fifteen additional dolls, each with new abilities.
Their press release sums up the content's plot with these words:
In The Lost Hobo King, Charlie travels to the kingdom of Camelfoot to help his hobo friend Levi with an important family matter. Levi’s uncle Rufus, heir to the throne of Hobo, may only take his rightful place if the lost crown can be found. To recover the fragmented crown, Charlie must use his unique talents to overcome several tests of valor left by the ancient hobo mystics. It is only then that the ancient crown can be re-forged, Rufus crowned, and the fractured hobo people united under one sardine.A price has not yet been confirmed for the content, but it will add new achievements (which you can see for yourself here: The Lost Hobo King for Stacking).
We've got the full list of Stacking achievements - check the list for guides to unlocking them.