This is an easy way to get the Dunes of Despair mission + bonus with lots of time to spare and without cheesing the mesmer boss. It's likely the way the devs intended the bonus to be done. This method is sort of described on the wiki, but not very clearly, and jumbled in with a bunch of worse alternative methods.
- Take the low ground in front of the Ghost (Point G).
- 2x Forgotten Arcanists enter the main fort at Point 1. Let them come to you, then kill them.
- 2x Forgotten Arcanists enter the main fort at Point 2. Let them come to you, then kill them.
- 2x Forgotten Arcanists enter the main fort at Point 3. Let them come to you, then kill them.
- 2x Forgotten Arcanists enter the main fort at Point 1. Go to Point 1 and kill them.
- You may wish to kill the wurm at Point 1 now. Usually it cannot reach the Ghost, but in some unlucky instances the Ghost will pick a position on the throne that's just close enough the wurm can get him. In this case, you will fail the mission if you don't kill the wurm.
- 2x Enchanted Bows enter the main fort at Point 3. Go to Point 3 and kill them.
- 2x Enchanted melee (random mix of Enchanted Hammer and Sword) enter the main fort at Point 2. Go to Point 2 and kill them.
- (At this point there should be over 7 minutes remaining.)
- Exit the main fort at Point 2 and go towards Point 4. If you go straight towards Point 4, you will encounter several annoying scarabs, but easily intercept the upcoming boss. You can also hug the outer wall of the main fort, then cut across towards Point 4. This avoids most of the scarabs, but the boss may get away if you cut across too late.
- A boss group will exit the side fort at Point 4 and seek to enter the main fort at Point 2. Intercept and kill it. Have a longbow ready to aggro it from afar if it starts moving before you're in position. (Longbow is preferred over flatbow here because of the moving target.)
- Go to Point 5 and kill the scarab pop-ups there.
- Use a longbow/flatbow to pull the boss group at Point 6 over close enough that you can fight it with your ranged party members standing at Point 5. Kill it.
- Killing the boss group from Point 6 triggers a spawn of 3x Forgotten Cursebearers at Point 5, who will seek to enter the main fort at Point 2. However, since you are standing at Point 5, they will immediately aggro and you can just kill them.
- Go to Point 6, cross the bridge into the side fort, and use a longbow/flatbow to pull the boss group at Point 7 as close to the bridge as they will come. Then kill them. As soon as the boss group is dead, run back across the bridge.
- Killing the boss group at Point 7 triggers a spawn of 3x Forgotten Illusionists at Point 5, who will seek to enter the main fort at Point 3. You should be able to aggro them with a longbow from the bridge near Point 6. (Or flag someone back during the preceding boss fight. Or leave some spirits in their path to delay them.) Be ready to flag heroes/henchmen out of triple Chaos Storm, and kill them. (Again, longbow is preferred over flatbow here because of the moving target.)
- Go kill the boss group at Point 8.
- (The bonus is now complete. At this point there should be ~1-3 minutes remaining.)
- Killing the boss group at Point 8 triggers a spawn of 3x Enchanted melee (random mix of Enchanted Hammer and Sword) at Point 9, who will seek to enter the main fort at Point 1. However, you can get there first by entering the main fort via Point 3. Then either go to Point G to wait for them, or Point 1 to intercept them.