@Heather-Foxwood It sounds like complicated one for my experience. But I assume that they would like to use the art for promotion materials, merch and so on in the future without paying you a procentage. Probably you may ask them to find a solution so both sides to be satisfied. If you don't care about these profits, maybe they should be specified and mentioned in the contract and give the rights to use them and also mention that you will still having the rights to use the art but with no comersial purpose/ financial profit. I know is the same like giving the rights, but ot will feel better and will secure you if in the future they want to use them for something not included in the contract. ( like a movie or something). These are just thoughts, I am not a specialist. 😉 And good luck!