BwerWahHAHAHAHA!!!!
I killed the Black Dragon in two rounds thanks to my Sorcerer, here's how.
Using either Limited Wish or a Scroll bought from Ribald in the Adventurer Mart, cast Chain Contingency and store 3 Abi-Dalzim's Horrid Wiltings in it. Set the conditions to trigger when enemy is sighted and cast to nearest enemy.
I had Odin Magnus, my Sorcerer, Jaheira, Imoen, Anomen, Keldorn and Jan in my party.
Anomen and Keldorn were not involved in the fight other than waving their weapons and taunting the Black Dragon.
Here's what happened... ...
The party, accompanied by 2 Aerial Servants, 2 Mountain Bears and 1 Fire Elemental, walks up to the Black Dragon and start talking smack to him. The Black Dragon of course, gets mad and goes hostile, the battle begins.
Round One:
Odin, Jan and Imoen starts casting Lower Resist, Jaheira casts Insect Plague while Anomen, Keldorn and the summons move in to engage in melee.
Black Dragon casts Entangle and counters with Wing Buffet, Anomen, Keldorn and the summons all get knocked back before they get a chance to hit the Black Dragon.
Odin's Chain Contingency finally triggers, Black Dragon gets really desicated as the 3 ADHW suck the moisture out of it.
Round Two:
Jaheira casts Lightning Storm and
*ZAP!*, Black Dragon is defeated.
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If not a Sorcerer, then a Paladin.
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Baldur's Gate Item Mart