From Destinypedia, the Destiny wiki
(Note:This is 1800 power but the mission can bump you up to 1790 for it.)
In order to start the mission, you need to walk into 6 total vex cubes to generate a passcode. Once in you will need to go through holes until you reach a purple vex domain. This is a puzzle where you need to shoot vex oracles in specific order depending on the shape to progress, there is no downside to getting one wrong.
After this just move until you reach the first boss.
You will need to kill headless goblins to get motes to protect yourself. The first phase is 8 then 10 then damage.
The second phase is 10 then 12 then damage.
After killing him you will need to jump across a chasm.
Then start platforming until you reach the final boss.
Brakion, Repurposed Mind
In order to damage him you need to kill a daemon then do the shape puzzle then damage.
Do this 1 more time and then just kill him normally on the 3rd phase.
Collect the chest/sword and you are done.