gotta get your resists up. Resistance is on a scale of 1-100%, so if you have 80% resists to lighting and fire, you will take very little damage. also, use the shift key to pan your view, so you can cast spells on him before he sees you. If you have them, either curse (cast several times in a row) and then freeze, and then life leech works well to weaken him considerably without any retaliation. you could also try blind on him too. finish off with whatever you like; hellspike is good.
it is not on a 0-100% scale. Just the more you have it, the better. There are no limits for res. number.
