Check out the fan art thread here
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I'm pretty sure people have shared the assets from the game and have discussed how to get started making fan art so give the whole thread a read. I'm sure if you ask for further advice they'll be helpful. Most people seem to cut and paste characters from the game because the actual painting process is so time-consuming.
There's also some really good stuff in there for anyone else who's starved for game content right now. Specifically the fan art by Saberlocked (
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) and Hefelo (
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) is fantastic.