Click here for the Adventure Time Wiki's entry on The Great Mushroom War
Anyway, I wanted to give The Young Lad something Adventure Time-y for his room, since he doesn't have anything, but to be blunt, I'm crazy broke. Papercraft to the rescue!
The Cartoon Network website has lots of cube-y models of characters from the show that you can download, print out and build. Here's the link:
In the top row, from left to right, we have Lumpy Space Princess, Finn the Human (possibly the last human, for those not familiar with the show), Jake the Dog, and Beemo, their sentient game system. In the middle is Ice King, with Marceline the Vampire Queen on his left and Princess Bubblegum on his right. On the bottom are two of the many princesses reigning in the various kingdoms of the Land of Ooo. The Young Lad didn't have a preference, so I chose my favorites: Ghost Princess and Raggedy Princess. They are definitely the two coolest. I mean, it doesn't get much more badass than using the shard of glass stuck straight into your head as your crown. And that's Lady Rainicorn up on top, who I had to print out as a regular image, because there's no paper model for her yet that I could find.
The minute I finished this thing, it went up in The Young Lad's room, and he went to sleep with it slowly spinning above the end of his bed. The bottom line is, if you can't afford to buy stuff, make your own. Surround yourself with things that make you happy, even if they're makeshift versions that you cobbled together yourself. We all need a pick-me-up these days.