1. Can we make changes on character design?
2. Can we recreate characters from old games like contra, mario etc? Basically 8bit to 3d?

Hi, Yes and yes, there are no limits for your creative ideas.

So can we use existing concept art from video games? or take inspiration from them?

you can use existing concept art

thank you Humster, it is really good news for me too 🙂

Creating video games can be quite challenging as the developer always needs to focus on creating something new and would prefer to ensure that there is a good demand for the kind of video game he or she is planning to create. You can also go through with some useful reference of video games or PC games so that you will have some idea.