Indie game storeFree gamesFun gamesHorror games
Game developmentAssetsComics

It says in the License, "Licensee may not superficially modify the game artwork and sell it to others for consumption, reproduction or re-sale." Does this mean I can modify it and use it in my game only? Or can I not modify it at all?

You can modify for the purpose of your project, correct. You just can't edit and then re-sell the artwork itself.