[SilverBear]

Once you have his defenses knocked down you need to start hitting him with everything you have. And I do mean everything including the kitchen sink +3. Since he will regenerate quickly you have to hit him with heavy duty weapons and offensive spells. It never hurts to hit him with a couple lower resistance spells and then load up If he is spell sequencer with Melf’s Acid Arrow, Flame Arrow, Chromatic Orb or whatever your favorites ones are. My favorite tactic is to occupy him with Mordenkainen’s Sword and a couple other heavy duty summons.
As far as equipment goes; don’t be shy about using lightning wands on him, what are you saving the charges for anyway? Ring of the Ram is always good for knocking an opponent down, which is why I always have two of them.