The biggest problem to fight this boss is reaching his location, as the upper floor of the djinn tower is FULL of efreets, with their summons, they can bring down a level 80 knight in a strong combo if all are lured to the stairs, bring the best potions you can drink and heal whenever your hp gets lower than 800, Elven Amulet is STRONGLY recommended to go up this last floor (although the efreets will deplete it within 5 seconds average), might ring can be useful for lower level vocations, it's not recommended to go up the last floor for levels below 80. You can consider this boss as a stronger Efreet with a lot of hitpoints. Any vocation should kill him quickly before his summons increase total damage.
Knights: Since moving is not necessary while fighting him, you bring a strong two handed weapon and wear a Sword, Axe, or Club Ring while fighting him and wear your Dwarven Ring later. Also, bring along some mana potions to attack him with berserk, heal if your hp gets below 500, and 800 if he has both summons.