I'll admit, Sephiroth isn't that hard in KH2, but this guy completely owned him. I can thrash him in under a minute by spamming Trinity Limit and following up with an eternal combo while Berserks in effect, but this is just beyond crazy.
EDIT: His videos are from the Japanese-Only 'special edition' of Kingdom Hearts, thats how he fights some bosses you probably havn't even heard of.
Got any other really good gaming videos worth sharing?