>>92247181Well plenty of custom sprite sheets are based on existing ones.
For example, the Toph one they used was a collaborative effort from fans to get her on the show and they modified a Sasuke sprite sheet for it.
One of Death Battle's animators does have contact with a guy who makes custom sprites (his work is shown in Natsu vs Ace and Shovel Knight vs Scrooge McDuck)
Other examples would be fan made mugen sprites you can find online