how do i beat sullivan in dead rising 2?

Answer 1

Bring strong melee weapons and good foot items. Your number one goal is to not get knocked off the platform. Your number two goal is to hit Sullivan. Seriously, getting knocked off opens you up to zombies and his ranged attack. You don't want to be down there.

Sullivan is very quick and mobile, you need to be, too. Use the double leg drop kick. Always be drop kicking. He can't knock you off while you're doing it after you hit him a couple of times with it, he'll take a knee and you can use your melee weapons.

Answer 2

If you have time to spare you can leave the arena you are fighting him in and when you return he will be at the same health level as you left him.  Use this to go down to the closest casino floor, in the middle, ontop of the big gambling machins is a LMG.  Kepp going back for that and collect heath packs.  Stay by the entry way and try to pick him off with the LMG.