in a long past patch d2 got added stuff to do. One of them was to hunt down a 'randomly' appearing super diablo called diablo clone. He's much tougher than any of the other bosses, until the next added content and i think they put in other elite boss versions for more cool treasure (tourch).
Odd how so many people are still playing just in this thread. I anticipate d3.
Yep, but maybe not as random as you might think
For everybody else not still playing d2: When he spawns, it's in all games on a server that are in hell difficulty mode - the first super-unique monster that any person comes upon in that game instance turns into the diablo-clone (super-uniques are monsters that are 'named' and always appear in the same place in every game). Killing the diablo-clone drops the annihilus unique charm, an item that gives bonuses while kept in a character's inventory (no other monster drops it).
The spawning depends on a counter which is kept for each server, the particular server is chosen at random when a game is created. The counter is increased whenever a Stone of Jordan (unique ring) is sold to a merchant on that server - the SoJ cannot be bought back and it takes 75-120 sojs to spawn the next d-clone (all games in all difficulties on that server receive messages when sales are made). This is usually done by groups of people that can amass enough sojs to sell and can recoup the cost through obtaining several annis (the charms) from that spawning.
Whenever there's a duplication hack, sojs are a very common item to duplicate. This d-clone scheme was mainly introduced to reduce the volume of dupes floating around while the hacks were fixed by subsequent patches.
http://counts.dcloneirc.net/
http://www.dclonehunters.net/index.php?orderby=up
Also anticipating D3 for the last 5 years or so; oblivion mods and torchlight are still holding me over till 2011.