It is possible for Cloud to beat the game in a single character challenge using initial equipment and no materia. Cloud can beat 2 of the 4 weapon as well.

Edit:

Figured i should add a linkhttp://db.gamefaqs.com/console/psx/f...vii_scienm.txt

Sephiroth with a whole party is very quick to beat it took me only a few min to take him down. The longest part was sitting the Nova spell out hoping it would finish before im a grandfather.

Cloud also has a much better sword then the starting one that is provided in the challenge, the ability of the fighting game he is in and kingdom heart which is more then enought to obliterate Samus.