Thank you for the question.
My phone has a lasso tool that I use to remove the background and make it a transparent PNG
Afterwards, I moved it on to my PC to use gimp. In gimp, I first go to filter then blur then pixelize and make it 4-bit.
After that, I go to colours and use colourize to give colour because I only used a big piece of white plasticine I have for all the art in the game (except the artifacts) .
Then I play around with posterize to finish it.