This achievement can be acquired solo at level 90 and is fairly straightforward.
To note: Archavon must be started last, as his lunge attack will cause the other bosses to despawn.
First, clear the trash in front of Archavon, Emalon, and Koralon. Kill Toravon the Ice Watcher now if desired, as that boss is not part of the achievement. Once the trash is clear, go back to Emalon or Koralon and get started on them. Stop DPS on each at 15-20% health, then drag both of them to Archavon. At Archavon's room, immediately blow him up. Archavon has 2.3 million health in 10-player mode, and uses the lunge attack every 45 seconds, so 51,000 DPS is required to kill Archavon before he causes the other bosses to despawn.
- Patch 3.2.0 (2009-08-04): Added.