Hi Ruprecht! I assume this is for selling on the Roll20 marketplace? Many marketplace creators use the 2014 statblock and character sheet in their modules. It is to Roll20's advantage for you to do this, since it encourages players to play/purchase your campaign on Roll20. It's always a good idea to consult a copyright lawyer for any gray areas, but sticking to the SRD is generally pretty safe, especially since it has now been released into creative commons. If you have any specific questions, I'd suggest going to the Marketplace Partner Help Center and read through the articles there. You can also apply to the Marketplace creator's Discord and get much better advice from people who have already done exactly the sort of thing you are talking about.