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One of them is to do those modifications yourself. It requires having some familiarity with the engine, in order to find what you need to change and what not, but it is doable. Doing it this way also allows you to tune the parameters to your liking. The 2D game art you create has to align with the target audiences preferences For instance, if you are aiming to create a simple game with easy-to-learn and master mechanics that are targeted toward children, then making a 2D game art that is elaborate would be unnecessary. It may even end up negatively affecting the game.