I'm not all too familiar with character infringement and all of that, but from what I understand you can purchase a pre-made mickey mouse character for example and place it on a cake if you were to sell it and that would be alright. However, I'm looking to make a special symbol from a video game for my uncle's birthday cake, but I wouldn't be selling it to him ( obviously that'd be kind of messed up ._. ) it's going to be a surprise, at home cake thing as well as it being on top of an xbox cake. So what I'm really asking is if it is technically legal as long as I'm not selling it in anyway to make the symbol and xbox cake...?

sure if you're making an edible creation for a family member's birthday you can make that -- if you also have a cake business do not display pictures of it -- it would come under fair use as the game is part of our culture/world --

just like we can make Minnie mouse character cakes with the Wilton cake pan but not sell them nor display pictures