Introduce

Chaos Tristram, also known as Uber Tristram, is a special area that can only be accessed during the Pandemonium Event, it is an exact replica of the destroyed Tristram found in Act I and is the location where it takes place. Hardest boss fight in the game. The area uses the same preset map as the regular Tristram. It is visible through a red portal similar to the regular Tristram, but this portal was created in Harrogath by taking the horn of Diablo, the Eye of Baal and the Brain of Mephisto, are found in other special areas related to this event. So the player must take on the task of defeating the combined forces of the Almighty Demons: Uber Baal, Uber Mephisto and Pandemonium Diablo.
Note: Considering that the Pandemonium Event is a mission that only opens Battle.net and is not available in Single Play (aka offline play) or even opening Battle.net, the player must install PlugY (Extension Crack of the game). It is not generally considered part of official lore.
After the Succubi Legion, her strongest and only daughter Andariel was killed by the mortal who had successfully defended the Worldstone, Lilith, Queen of the Succubi and god of all demons, swore to personally intervention. She masterminded Diablo's resurrection by manifesting herself in the mortal realm and performing a Shadow Summoning ritual.
This ritual, long thought impossible to perform by the most powerful mortal mages, allows Lilith to bond with Diablo across the realms, strengthening Diablo until Diablo can finally reincarnated again in the mortal realm. Rage and a deep desire for revenge flared in the Sovereign's eyes, Diablo and Lilith revived the two remaining Prime Demons as well as Duriel and Izual, two of their strongest guardians.
Diablo announced his grand plan – the three were finally strong enough to spread Pandemonium throughout Sanctuary. The Three amassed their forces at a devastated outpost in the mortal realm – Uber Tristram.
Only here can the heroes hope to defeat the Evil Trio once again and save Sanctuary from destruction.
Once you have all three Master Keys, you can return to Harrogath and convert them in the Horadric Cube. This will create a Portal to Uber Tristram.
Uber Tristram has the same base structure as regular Tristram but has a horde of hellish monsters, such as rare and powerful Balrogs. There are also a variety of Unique Monsters, Champoins and Uber Prime Evils minions. The main goal when the player arrives at Uber Tristram is to find and defeat Uber Baal, Uber Mephisto, and Pandemonium Diablo (so called because Uber Diablo already exists).

Keys:

The first step is to collect the three keys needed to open the first of the red portals (Red Portal). Keys of Hate, Terror, and Destruction are required, and can only be found from certain Boss Monsters and only on Hell difficulty.
Key of Terror from The Countess (Quest 4 Act I).

Key of Hate from The Summoner (Quest 5 Act II).

Key of Destruction from Nihlathak (Quest 4 Act V).

You should have 3 of each key before starting the second phase of the Pandemonium Event, so you can do all three Special Areas in 1 Room. (The same area will not be repeated in the same game, so you will have all 3 ingredients for Uber Tristram: Key of Hate, Terror, and Destruction).

Key of Hate.

These are used by The Countess, who is located on the fifth floor of the Forgotten Tower in Black Marsh, Act I. The Countess often runs for her Runes, and will drop the Key of Hate. around 8% time The Countess died on Hell difficulty.

Key of Terror.

The Summoner drops the Key of Terror. The Summoner is found at the end of one of the four locations in Arcane Sanctuary, Act II. The Summoner will only drop the Key of Hate on Hell difficulty

Key of Destruction.

Nihlathak will occasionally drop Keys, but only on Hell difficulty. He is found at one end of the four-winged Great Hall of the Halls of Vaught, on the 3rd floor of the Halls through Anya's gate in Harrogath, in Act V.

Open Red Gate Special Areas:

Once you have the keys, stand in Harrogath, on Hell difficulty, put one of them (1 Key of Hate, Terror and Destruction) into your Horadric Cube and Trans. A red portal will open to one of three locations, Matron's Den, Forgotten Sands, and Furnace of Pain. Which gate opens first is random, but if you do all three in the same room, you won't get the same one twice.
For this reason, you should have 9 Keys (3 of 3 types) to start with, 3 Keys each so you can do them all in the same room.

You should also stand in different places to spread out the three gates, so they don't overlap and make choosing the right one 'difficult' (There are quite a few newbies who don't understand this issue and the result is well known to everyone. r =]]z).
You will add a 4th gate after completing these three gates.

The Matron's Den:

Lilith drops Diablo's Horn, one of three items needed to open the portal to Uber Tristram.

The Forgotten Sands:

Uber Duriel drops Baal's Eye, one of three items required to open the portal to Uber Tristram.

The Furnace of Pain:

Uber Izual can Teleport, and often spawns with some very nasty Monsters. He drops Mephisto's Brain, one of three items needed to open the portal to Uber Tristram.

Uber Tristram:

To create a Red Portal to Uber Tristram, place Diablo's Horn, Baal's Eye and Mephisto Brain in the Horadric Cube, and Transpose them while standing in Harrogath in a Hell difficulty room. A red portal will open, the fourth in that area if you have completed them all in the same room. It will take you to Uber Tristram, where the real fun begins.

Information of Uber's three giants:
Uber Mephisto:

A deadlier version of the regular Mephisto. Uber Mephisto comes with Conviction Aura at the highest level that will reduce the maximum resistance to negative values and a variety of elemental attacks including Blizzard and Lightning. Uber Mephisto's resistance is also very high, and Uber Mephisto often spawns minions such as Skeleton Mages and Archers.

Pandemonium Diablo:

A "tank" for Uber Baal. Much stronger and faster than regular Diablo, and uses the Bone Prison and Firestorm skills to cause death. Pandemonium Diablo can use Armageddon, skills Druids, raining fire down on all of his attackers

UberBaal:

Quite similar to Baal in Hell mode. Uber Baal has more, including Mana Rift, Hoarfrost, Incineration Nova, etc. Also can Teleport and clone yourself

Reward:

Once you kill them, the last one to die will give you Hellfire Tourch, a Large Unique Charm as well as a Standard of Heroes. Standard of Heroes is a symbol that you have successfully completed this quest, and if it is in your inventory at level 90 or higher, you will not lose experience when you die. (Many people don't know, but I'll write it down to let you know =]]z).

Information :
Hellfire Torch unique large charm
+10-20 To All Attributes
All Resistances +10-20
+3 to random character class skills
25% Chance To Cast level 10 Firestorm On Striking
Level 30 Hydra (10 charges)
+8 to light radius
Required Level: 75
Standard of Heroes
Don't underestimate it =]]z it gives you the ability to not lose exp when you reach level 90 or higher ^^

Pandemonium Event Tips:(Tips)

All characters in the game must be in Act V.
It is not necessary to kill Baal Hell before proceeding with the Pandemonium Event.
Spread out the Red Portals in Harrogath for easier access.
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