One player has officially beaten Diablo 3: Reaper of Souls a mere five days after its launch.  They managed to defeat Malthael, the end boss of the expansion, on Torment 6 difficulty in Hardcore mode. 

Torment 6 is the highest setting in Diablo 3's new difficulty tiers.  At that level, monsters' health is at 8590% the amount they'd have on Normal.  Their damage is boosted by 2540% as well. 

Playing the game in Torment 6 in Hardcore mode makes it even more annoying.  Characters created for hardcore mode aren't allow to respawn.  If they die, they're lost permanently along with all of their equipment. 

TheFriendly15, the masochist who beat Malthael on Torment 6 Hardcore decided to stay on the safe side.  There's no time limit for the fight so he sacrificed damage for durability.  His gear's been loaded up with Elemental Resistance gems.  The character's Toughness is listed at 50 million in one of the kill screenshots.  You can see his talent build for the fight on his Diablo 3 account profile. 

Wearing down Mathael's massive health pool using this defensive setup was a long process, though.  Way longer than most players could stomach. 

Unfortunately, there's no video of the kill.  He said that he's unable to record video on his computer without lag.  We'll have to wait for someone else to kill Mathael on T6 HC to see the fight ourselves. 

Dedicated D3 players still have one other world-first accomplishment to strive for.  TheFriendly15 actually played through most of Reaper of Sousl on Torment 2 before switching to Torment 6 for Malthael.  That means no one has played through all of the expansion on the highest difficulty of Hardcore mode.  The race is on to achieve that lofty goal.  It took about a month before players pulled it off in the standard D3 campaign. 

Reaper of Souls introduces Act V to the campaign along with a new Crusader class.  Once players have beaten Act V once, they can play an Adventure Mode with randomized quests and dungeons.  The expansion was accompanied by a huge patch that revised the loot and Paragon systems, among other things.  If you still haven't bought Reaper yet, check out my review to find out my opinions on it.