Fire God Dungeon/Guide

It's recommended to beat the Fire God Dungeon with Ranged, since enemies here are all melee and magic, due to the Combat Triangle.

Item	Slot	DR%
Aeris God Helmet	Head	8%
Aeris God Platebody	Body	8%
Aeris God Platelegs	Leggings	8%
Aeris God Boots	Boots	8%
Aeris God Gloves	Hands	8%
Subtotal		40%
Infernal Cape	Cape	4%
Fury of the Elemental Zodiacs	Neck	2%
Aorpheat's Signet Ring	Ring	0%
Dragonfire Shield	Off-hand	8%
Total		54%

Since you need a large amount of DR, using Damage Reduction Potion II (or better), or Stone Skin to get the last bit needed.

For the weapon, Ancient Crossbow is a decent choice, with Emerald Bolts, as you will need Diamond for potions.

If you haven't grinded Fury of the Elemental Zodiacs yet, you could use Elite Amulet of Defence, or at the very least Silver Diamond Necklace instead, with the same DR% stat.

You could use Earth Layered Shield instead of Dragonfire Shield, which would give you 4% more DR, and a Silver Diamond Ring. Which could be enough to idle it without prayer or potions.