The key word here is A "Full" download of Cartoon Fighters V21 means you aren't just getting a demo or a beta. You are getting the complete package:
Would you like a full character roster or stage list for v21 as well? cartoon fighters v21 mugen full
V21 usually comes with a custom "Cartoon Network/Nickelodeon" themed screenpack. If you see a black screen on launch, delete the data/save/mugen.cfg file and relaunch the game to regenerate default settings. The key word here is A "Full" download