In the game, you can use food or drink for additional buffs, and the best buff to get for this dungeon is the one that deals double or triple damage against the enemies. One of the keys in reaching the highest level is to dish out as much damage as you can to clear the dungeons fast. Movement speed food is ideal to cut the wasted time on walking. Elixir of Flame deals additional 10% damage to flame attribute targets for 20 minutes. The potion requires 5 Crest of Flame and 1 Alchemical Powder to make. Keep in mind that you need to be level 60 or higher to use this potion. Each class members can cast their class party buffs, which will buff the entire party. Coordinate your party mate to make sure that no one will cast overlapping buffs. Note that you need to recast the party buff every time you pass the next hall after defeating Zaahir, since the buff disappears every time you go through the portal.

Summary:
Buy food and drinks. Craft Elixir of Flames. Use class party buffs.