From Path of Diablo Wiki
The follow changes to bosses have been made in Path of Diablo.
- Description: The Diablo Clone fight is a special encounter first introduced in Kyanite #11. It is meant to be a very difficult challenge for endgame players. If you can beat him you will be rewarded with the Annihilus unique small charm.
- Requirements: Diablo Clone cannot be spawned by selling Stone of Jordan rings to the vendor (unlike in regular battle.net). Uber Diablo's realm can only be entered through a specific item called "The Infernal Trial" which can only be created by using the Horadric Cube. Use it like a regular map item in the "The Ancient's Temple" in Harrogath (NOTE: once opened, you cannot go back to town and reenter the fight).
- Cube Recipe: In order to create the special map item, you must gather: a full organ set from the Prime Evils, a Soulstone that drops from Diablo in Uber Tristram, and a Key of Chaos that drops in maps. Put all ingredients in the cube to create "The Infernal Trial".
- General Mechanics:
- Diablo Clone spawns from a hooded man ("The Dark Wanderer") which is standing in the middle of the map. When you are prepared, move towards him to start the fight.
- In the first phase, Uber Diablo is immune to all damage and curses and spawns a huge amount of minions alongside him to fight you called "Reanimated Warriors" and "Undead Commanders.
- Reanimated Warriors are monster type 'Reanimated Horde' but are modified with high physical damage and crushing blow chance. They no longer have a charge attack. They are also immune to curses and are highly resistant to all damage types.
- "Undead Commanders" are mini bosses classified as 'Prime Evils' for gameplay purposes. They are ranged undead creatures that also have high resistances, Holy Freeze aura, and attack with Guided Arrow magical damage. You must defeat all five Undead Commanders to progress into phase 2 of the Diablo Clone fight, where Diablo loses his immunities and becomes vulnerable to damage.
- During phase 1, Diablo is still able to attack and damage you constantly. Again, you cannot damage him until you defeat his Undead Commanders. Diablo also emits a special red aura that reduces all the player's, minion's, and mercenary's maximum resistances by 5%.
- Diablo Clone now has more life that his predecessors and a portion of his ‘Fire/Cold/Lightning Resistances’ have been replaced by ‘Fire/Cold/Lightning Absorb +%’.
- Damage types during this encounter include Fire (Armageddon) and Magic (Hose) (Diablo Clone), physical (Reanimated Horde) and magic (Undead Commanders).
- Drain effectiveness changed from 0% to 10% (it is possible to leech now from Mephisto without using the Life Tap curse)
- Now uses 'Lower Max Resist' curse which does -5% to player’s max resists
- Now uses Frozen Armor instead of Chilling Armor
- Lightning hose attack is now much more dangerous (damage increased, can hit melee characters, 33% phys damage and 67% lightning damage)
- Has ascended and earned the modifier ‘Prime Evil’ (this basically makes him like the act bosses and other ubers who have special resistances and damage reductions)
- A3- Council Members can no longer spawn with Fire Enchanted (fixes bug in Vanilla D2 that causes these monsters to deal insane damage in Nightmare)
- A5- The Ancients will always spawn with fixed modifiers: Korlic has increased physical damage, Talic is extra fast and Madawc has multiple projectiles. Talic now uses a lower level Whirlwind.
- Uber Tristram has been reduced in size and several obstacles have been removed