How did you kill him? I played so many mages but never a really evil one.
Like this:
By buffing up and beating him with a stick and mirror image?
Only makes sense considering his 98% MR makes offensive spells useless.
The real problem lies more in getting your Thac0 low enough to hit him reliably and then being able to do enough damage when you do hit him rather than putting up defensive measures (although buffing your AC as much as possible is still pretty significant so you don't have to waste time re-casting Mirror Image).
I'll leave it up to you to figure out the overall gear/buffing scheme... but I'll give you a two hints:
1) Knave's/Adventurer's/Traveller's Robes (whichever gives +1 AC vs. slashing) are better than Robes of the Archmagi
2) You'll want to buff your STR for the bonus to Thac0 and damage.
Shandalar is most easily killed by using a few vampiric touches and magic missiles on him iirc.
IIRC, Vampiric Touch requires a to-hit roll, so you'll need to crit with it a couple times in a row between re-casting it. In theory, I think it'll work, but it's far from ideal, as is the wand (though I wouldn't go so far as to call it cheese).
The problem with Shandalar is he doesn't cast his spells, but rather is script-triggered behind the scenes to fire off the major damaging spells in the game faster than would normally be possible, and the script also makes it so they can't be interrupted (IIRC). Plus, he disappears at the end of the script, so you have a limited amount of time to take him out.
I did it like this:
Gear/Buffs:
Potion of Insulation (Immune to electricity)
Potion of Magic Shielding (saves always succeed, damage from spells reduced 50%)
Potion of Magic Protection (+50% Magic Resistance)
Robe of the Archmagi (+5% Magic Resistance)
Cloak of Balduran (+25% Magic Resistance)
Combat Sequence:
Round 1-- He's still neutral, I cast Magic Missile at him.
Round 2-- He casts Globe of Invulnerability, I cast Dispel Magic to get rid of it.
Round 3 thru end of battle-- script starts slinging useless spells-- Mostly lightning bolts (I'm immune to electricity) or save-to-negate spells (saves always succeed), and anything else is handled by 80% MR and 75% spell damage reduction from auto-saving for half-damage, and having it cut in half again by the potion. Meanwhile, I just plaster him with Magic Missles till he pops.
All in all, takes me around 6 MM's total and 1 Dispel Magic, while he takes at most a third of my HP off (20-ish HP), and kills a bunch of commoners and innocent chickens.... OH! THE POOR CHICKENS!!!!!