Fanfiction is easier to write than regular fiction, because the characters and world are already invented. For the Adventure Time Game Jam last weekend, having a ready-made universe let jammers focus on making games! Here are three of my favorites:
There's not much to do, but the pixel art and writing is spot-on.
You need to take a fire pup back to the fire kingdom, but you're a snow golem and every time you touch him you lose your arms. Luckily pears grow them back.
Run around exploring and fighting bad guys, but you only have a minute!