[quote=@Renose]
Which mission is number 8?

Is that the one located where you fight the dude with the guitar?

Cause if so, the method I found was berserk charge and just jump and do infinite aerial combos. 
[/quote]

Number 8 is the one outside Yen Sid's tower where you have keep the bastard in midair for 85 hits. Like I said I tried Berserk Charge Aerial Combos but after reaching around 65 he just automatically starts falling down faster than I can reach him.