This feature will replace the world event
This is the raw concept
What's a raid quest?
Raid quests will take place in a dedicated arena-like level that gets unlocked when a raid quest is active. In this arena, players will battle against a very strong boss. This boss will have an incredible amount of HP, defense, etc. Defeating a raid boss will require a group of players. Once the raid boss has been spawned, players will have a given time to defeat the boss. The duration is still to be determined.
The boss will not be limited to Diablo's clone. Monsters that can spawn as raid bosses have yet to be determined, but I was probably gonna go with the three Prime Evils (highly buffed versions of course).
How is a raid quest activated?
This has yet to be determined, but just like the Diablo Clone World Event, it will be based on a random event. Once a player has activated the raid quest in his game, a notification is broadcasted in every games on the server. Of course, you will not be able to activate raid quests in passworded games. Raids can also be activated in games created in Destruction difficulty only.
Rewards
Rewards have yet to be determined, but of course the raid boss will at least drop a good bunch of sacred uniques. It might drop a charm as well, and maybe even rare reagents such as skulls and what not. I'd also like to implement a ladder for number of raids completed, along with a badge displaying in player's profile (probably a page in the stat screen)