Which dragon? They'res like 3 in game... on ol firkie?
use cloudkill on him if yur uber....... if not...... make sure fire resistance is at maximum, and grab all "dragon" items.... they sorta help, and get good ac (like -8 you'll be safe) and get that Dragon Bane +3- +6 to dragons found in the Lower Reaches, in the cult of the unseeing eye. Wands of Monster Summoning help as destractions to that bad boy...... dispell magic is also a must (or get a scroll of ruby ray of reversal) to disable spell protections.
God, I should make a site on dragon slaying!
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I am Tiamat!