When he starts spinning around, he swipes at you with his claw. You have to successful dodge 5 of these attacks WITHOUT using slow and he'll spin out and get dizzy, then you can attack him. You CAN use slow RIGHT before he attacks you so you can see where he's going to attack though, this way you'll know whether to duck or press up, but when you actually dodge the attack, it has to be normally, without slow on, otherwise it wont count and he wont get dizzy.