It used to be hard, but even before Silverfrost update I figured out his game. This is the first time you will seriously consider the cooldowns of your backstep, q and e dodge moves. If you are enough HM level, Ice veil fully maxed helps with heals too, and Ice shield comes in handy. Ice laser 3 also can stun him for 2 seconds, also good for control.
If he is doing his ice AOE, I used to grab him first and then look for a safe spot, then toss him with 2. He will try to get up and stumble for about a second or two, giving you breathing room/time to smack him with your harder hitting skills. I had around 370-380 ap the first time I beat him I think. Nowadays, I barely bother moving with 483 ap, I just put on Ice veil and laugh at his feeble damage.
Also when he is doing his red deadly AOE, backstep or q and e can come in handy, or you can use your ice shield first vice versa. These days I usually just backstep, then use q and e when he comes after me with the 5 hit combo. Well actually for the red AOE, you really shouldnt be that close anyways as a FM, and its range is so short I usually just walk out of it too, saving my actual dodges when he lunges.
For doing enough damage, I am fire build so I just use V C X (I skip Z, not really worth the bother), and then start laying into him with Fire laser 2 and RMB LMB spam, press F for either ice or fire/ fireicedragoncombo. Actually lay into him first with the fire/lmb to stack up the ember/orbits for max damage, and THEN use V C X for max efficiency. Again this is if you spec for a fire build. Make sure you dont have the explode stack path, that just cancels all your stacks and you'll do less.
Oh yea one last thing, don't fight him far range, fight him mid-close range, mid mostly, close when you got him stunned or knockdowned, back off into mid range again when he recovers. Its easier to control the fight this way, close enough to damage him/ he lunges less; far enough so he doesn't actually smack you.