The generic walkthrough is explained well on the wiki. Make sure to bring Ebon Vanguard Sniper Support as it eases up a lot of the encounters due to one-shotting foes.
You can walk to the Shrine of the Raven Spirit without aggroing any of the patrols.
Once you are there, a Destroyer Tremors will spawn. These are recurring throughout the mission and are best handled by casting Snipe, YMLaD, Wastrel's Demise and running out of their cast range for Wastrel's Demise to trigger. The accompanying Destroyers rip off quickly if you use a 25% IMS.
All destroyers can be handled with standard means (Melee (Kite), Ranger (LoS)), the Detroyers of Thoughts pose the only hard encounter. This tactic works well against them:
- Approach with Diversion, they'll immediately Hex Eater Vortex it, leaving you room for Empathy / Wastrel's Demise or Wastrel's Worry
- Bait their interrupt spell (20 second cool down)
- Diversion again to catch Guilt
- They'll heal themselves up heavyly with Inner Fire and Ether Feast - make sure to Complicate the latter
You can fully run through the second level.
Clear through the third level, approach the Asura Undergate and pull the Destroyers in batches you can handle. It will not spawn Mesmers, just Melee and Ranger foes.