I managed to beat him with buster sword, and everyone elses first wepon... He is not hard, and lev 70?... try 99. Alough you can easyly do it at 70, i knew some1 who done it at lev 47! which is suprizing!
I always thought if anything bizzaro sephiroth is easyer the the one you go against before hand.
Oh and surely you would have clouds ultimate wepon, if i remember rightly you just get it When you beat ultimate wepon!?!?!?!?!?!?