|Players of Hell difficulty Realm games are hereby warned that a new, challenging world-event has been added to Diablo II version 1.10. Players of Hardcore characters should be even more wary when encountering Superunique monsters during an active world event. Be prepared to execute a hasty Save and Exit, if your situation seems too dangerous.|
Diablo will spawn in every Hell game on a Battle.net server when a sufficient number of Stone of Jordan Rings have been sold to merchants on that server, in both Diablo II and Diablo II: Lord of Destruction, Standard and Hardcore, and Ladder and non-Ladder. Although the rings can be sold in any difficulty, only players in Hell games will see the message notifying them of Stones of Jordan Sold to Merchants. Anecdotally, every time 70-150 have been sold to merchants, players in Hell games see the message that Diablo Walks the Earth.
Diablo can replace any Super Unique or Boss monster that hasn't already spawned in a Hell game, allowing some control over where he is encountered. Spawning him in place of any monster that must be killed to complete a quest should be avoided, as it may prevent that quest from being completed in that game by anyone who still needs to do so.
While Diablo isn't Immune to anything, he has Damage Resist 50%, Magic Resist 50% and Resist 95% to all four remaining damage types: lowering the latter resistances with Lower Resist, Conviction and -% Enemy Resistance can drastically reduce the amount of time taken to kill him.
However, unlike the original Diablo, he can regenerate damage: since he has 642,700 base life, he regenerates at least 7,845 105/256 life per second (which increases by 50% with each additional player in the game at time of spawning). Poison damage, Prevent Monster Heal, Open Wounds and skills applying damage every frame (0.04 second), like Immolation Arrow or Meteor pyres and Fire Wall, can stop regeneration entirely.
He moves faster than the original and uses all the same skills, although some are actually slightly weaker. However, he has gained Diablogeddon, which is similar to the Druid's Armageddon. All level-adjusted stats (defense, Attack Rating, life , damage and experience) are higher than the original due to being level 110, which also makes him harder to hit with attacks.
He's most easily defeated by melee attackers capable of delivering Crushing Blow and benefiting from Life Stolen per hit or Life Tap, or delivering massive damage to a single target which always hits and cannot be blocked like an Amazon using Charged Strike. A Paladin using Smite also has the advantage of an attack which is fast, always hits and cannot be blocked.
The World Event can be completed more than once, and significant experience can be gained from doing so.
Diablo drops the Annihilus Small Charm upon his death. A character can only pick up this charm if one is not already present in inventory or stash. It cannot be transferred from one character to another by selling it to a vendor: once sold, it does not appear in the vendor's inventory and it's lost forever.