retrodude I wouldn't say no worries. I worked at Microsoft for 6 years and saw plenty of cases where they cracked down on developers for infringing on the property (trademark and copyright) of other developers. Especially when it is in the same category, a game with a character from a well known game that has brought MS and the developer a lot of money like Minecraft. Note that they already took two of his apps down due to this...
And especially when you make money off of selling a game with another companies characters. He made $100 for each game he submitted...
Just saying, it isn't so hard to make your own generic characters. It is however very hard to defend yourself if you use someone elses. And if you don't belong to a corporation you have no business protection, they can sue you directly for your personal assets.