If this is Castlevania and not Mario, I'm probably going to be gravely disappointed. Especially because we haven't seen a Mario cartoon series since the Super Mario World one. Also, keep in mind they say "most famous", and even though Castlevania is famous, I'm not sure if it is one of THE most famous video game franchises. So, it's equally possible it's a Mario cartoon.
And I'm really, really hoping it is, even if it'll probably be sub-par.