Clear it 100+ times to complete more township tasks, or earn a lot of .
Manual-Eating Build
The guide assumes that you have completed Volcanic Cave at least once, and have obtained the Ancient Claw. If not, then check out this Ancient Claw Guide for how to obtain this key item.
Before attempting Infernal Stronghold, it is strongly recommended that your Auto Eat threshold is higher than all of Malcs moves when you are not stunned. This build can achieve that with 900 HP, although it is advised to check it with the Combat Simulator to be sure.
The boss in this dungeon is Malcs, the Leader of Dragons (Malcs), and the strongest attack is the combination of Sealing (Stun) + Penetrating Claws.
The Ancient Claw can be substituted for the Sunset Rapier at a push, but due to the boss stun attack being very powerful, the faster you can attack after stun, the better your overall chances.
Use prayers to increase your accuracy, as without your hit chance against Malcs will be very low e.g. ~25% without prayers, compared to ~40% with. Using Diamond Luck Potion (any level) will give you a significant advantage.
Equipping the Infernal Cape after the first clear as this will increase DR, and will make it easier to get the 10 Infernal Claw needed for upgrading.
The DFS is one of the best defences against Malcs. However, for an extra increase in DR, consider equipping Silver Diamond Ring. Doing so will reduce your Dungeon clear time, but may increase your chances of survival. With DFS equipped as well as 990 HP it should be sufficient to clear this dungeon with ease.
Malcs Special Moves
Pay attention to the following special moves from Malcs:
Sealing + Penetrating Claws: do not underestimate this combo. The Spam Eating kicks in with a delay after you push a keyboard button, so it is important that you start before the Penetrating Claws hit you. This special move has two instances of damage separated by a short gap, so a good idea to use Spam Eating. The damage from Penetrating Claws is calculated as [math]\displaystyle{ 640 \times (1-\text{DR}) \times 1.3 \times 2 }[/math].
Sealing + Tail Whip: Heal to full HP before this hits, and if you have time, look what the max damage of the Tail Whip is when you are stunned. You may find that you can delay manual eating depending on whether your HP allows. The damage from this move can be calculated as [math]\displaystyle{ 690 \times (1-\text{DR}) \times 1.3 }[/math].
Sealing + Usual Attack: Occurs when Malcs uses two Sealing attacks in row. The approach given in Tail Whip works well here.
Sealing + Inferno: Not as strong as the other attacks, and one that you can normally rely on Auto Eat to survive.
Idling Options
This build relies on high DR and a high HP and the top tier of Auto Eat and uses melee as this gives a high amount of damage reduction (DR). If your consumables run out, then you will not survive, so be sure that you have enough in the bank before you begin idling.
Once you have sufficient DR to idle comfortable, you can also consider wearing the Chapeau Noir for a 10% chance of doubling the items received, which can reduce the number of dungeons needed.
Agility
Bonuses from Agility Obstacles can reduce the amount of DR required considerably by increasing your Maximum Hitpoints.
For instance, assuming the same Level 90 as before, after these HP bonuses, the DR required to AFK has dropped to only 54%. If you're lucky enough to have Finn, the Cat, hitting only Level 91 for a total of 1060 HP would let you drop as far as 53%, eliminating the need for either DR potions, or Prayers and Witch Summoning Tablets, or when combined with the equipment improvements mentioned above, both. Or used with everything above to lower minimum HP to Level 76, though using Cliff Balance and prayers together is costly.
After Water God Dungeon
With access to magic armor with late-game DRs, you can now take on this dungeon with proper Combat Triangle advantage, meaning no need for expendable resources besides food and runes, no need for agility boosts, and even still enough DR to spare some for item doubling.