Here are two drafts I made for the game's icon. They seemed good to me but when it came down to it, there was too much going on in both of these. I'm not a super great icon guy so doing these helped me learn a lot about what is important about making things recognizable on a much smaller size. I think the icons had to be readable at down to 30 x 30 pixels or something crazy.
The first thing is color. We obviously wanted people to recognize this game as an Adventure Time game right off the bat and in most people's mind, Finn is the main focus. So having the full range of the Finn colors in the icon was super important. The first icon was missing this and I tried a little harder to fit Finn's color range into the second draft. Even though I gave it the proper colors, there was still something really important the second icon wasn't accomplishing.
That brings me to the second important thing! Silhouette. The form of this character is mainly what defined Finns look and best represents the show. Even though I included the bear ears in both of these, that wasn't enough. So for the final icon, I made sure to include all the color elements that I could as well as a much more detailed silhouette including his arms, pack, ears and torso. With all these elements combined, Finn was fully represented even at the smallest size.