Ubers are portals to optional super bosses. The process of opening and using them is difficult and involved, but the payoff is the coveted Hellfire Torch.

The following is a brief summary of the process, to give you an idea:

You acquire keys to open portals. There are three different portals. The bosses, Uber Duriel, Lilith (Uber Andariel), and Uber Izual, in their respective portals, drop organs. You combine the organ set to open a portal to Uber Tristram. In the center of Uber Tristram are Uber Diablo, Uber Mephisto, and Uber Baal. The last of the three to die drops the Hellfire Torch.

Before you jump into farming keys and opening portals, you should be prepared and have an Uber Smiter built or you'll just be wasting your time.
If you don't, you may find yourself stuck in a situation where you can't kill the bosses for the organs. Uber bosses have massive life-pools over 600,000! You'll need Crushing Blow, Lifetap, and consistent fast-hitting high damage... and only one build can deliver all of that in a way that can kill these bosses quickly and that's a Smiter.

I'm going to list two setups that are flexible, as a guideline.
One is low budget and the other is optimized.

Low Budget Uber Smiter
Low Budget Smiters aren't likely to consistently do ubers without dying, but they will eventually get the job done. So expect to work a bit harder.

This build costs 30-40 FG (Non-ladder prices), has 100% Crushing Blow, max resistances in Hell Difficulty, and gets Lifetap from a wand on switch.

Weapon: Black {RW} Flail

Armor: Smoke {RW} Mageplate

Shield: Herald of Zakarum + Perfect Diamond for resistances (While it isn't truly low budget, it isn't expensive either, and your shield is too important to skimp on)

Weapon Switch: Wand with Lifetap charges (Can be shopped from NPC)

Helm: Guilames Face (Um'd for resistances if you can afford it)
Gloves: Laying of Hands
Belt: Thundergods
Boots: Goblin Toe

Amulet: Saracen's Chance
Ring 1: Ravenfrost
Ring 2: Anything with resistance & stats

Optimized Uber Smiter

This build should steamroll ubers with relative ease and will run you roughly 200 to 300 FG (Non-ladder prices).

Weapon: Grief {RW} Phaseblade

Armor: Chains of Honor {RW} Archon Plate

Shield: Exile {RW} Sacred Targe 45% Res Base

Helm: Guilames Face (Um'd for resistances)
Gloves: Crafted Gloves with 20ias & Crushing Blow
Belt: Verdungo's Coil
Boots: Goblin Toe

Amulet:  Mara's Kaleidoscope 
Ring 1: Ravenfrost
Ring 2: Anything with resistance & stats


                             So onto the first step: Acquiring keysets

A keyset is one of each of Key of Terror, Key of Hate, and Key of Destruction.

You theoretically could just acquire one keyset and open one portal, but that isn't smart, as it wont guarantee a matching organ set. The best thing to do is get three keysets, as two of the same portal can't exist in the same game. That means that if you open three portals in one game, you will get all three different portals and therefor all three organs for the set.

Keys can only be found in Hell Difficulty.
Key of Terror from The Countess in Act 1, Tower Level 5
Key of Hate from The Summoner in Act 2, Arcane Sanctuary
Key of Destruction from Nihlathak in Act 5, Halls of Vaught

These bosses drop their keys roughly at a rate of 8% or 1 in 13.

The Countess and Summoner are very easy to farm with strong characters, but Nihlathak can be very challenging to farm, even for some well-built characters.

                              Second is opening the three portals

As you transmute the first keyset in the cube while in Act V on Hell Difficulty, one of the following three portals will appear. (Do this away from the stash to avoid overlapping portals). You can open all three if you like, just make sure you don't make them in the same spot to over overlapping them.

Matron's Den
A large sprawling catacomb (Like the Forgotten Tower, but much larger) where Lilith resides
Kill Lilith for Diablo's Horn

Forgotten Sands
A waypoint-looking area (Like the Canyon of the Magi) and Uber Duriel will be very close by
Kill Uber Duriel for Baal's Eye

Furnace of Pain
A large area much like the River of Flame where Uber Izual resides
Kill Uber Izual for Mephisto's Brain

Izual and Duriel aren't that hard, but Liliths poison can be brutal if you aren't lifetapping.

                                             Lastly, Uber Tristram
Uber Tristram will be far more difficult than any of the Uber Bosses so far. Not only are Diablo, Mephisto, and Baal more damaging, but you have to face all three at once unless you're very careful about how you approach the center. I recommend you enter from the rear (The corner where Wirt's Leg is) and inch your way in until Mephisto comes at you. Hopefully you can run away and draw him out without catching the attention of the other two.

Mephisto is definitely the most difficult of the three, because he creates a swarm of skeleton archers whose damage is nothing to scoff at, and his lightning orb can 1-2 hit even some of the toughest characters. Once he is out of the way, you can try to lure another one out alone, but it's difficult to do.

I find that, with the optimal Uber Smiter, I can just run right into the center and take on Diablo and Baal by constantly life-tapping the closest thing to me (Preferably one of them).

Once you kill the last one, congrats on the torch!




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