If you are on a gamejam with short time and you need some pixel assets you can use PixaTool that easily help you to convert images/videos into 8bit / Pixel style.
So you can use 3D render images, illustrations or painted images to give that PixelArt feeling. Also have batch processing and can export videos, look the info in the official page and their tutorial to learn how they are done.
Here is an example of the conversion quality
Software link: https://kronbits.itch.io/pixatool
Hope you like it! 
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