Phase 1: Defend the Machines in The Vault of Glass
In the first phase you just have to defend machines from hordes of Vex. At this stage the Templar cannot be damaged. First you need to defend one, then two machines. After this you will receive a message saying “a horde is coming.” Many Fanatics will spawn. When you kill them a green aura appears on the group. When you walk into it you get marked. When the Templar activates his nuke ability you will instantly die. To cleanse yourself from being marked go into the light fountain in the middle. After this you need to defend 3 machines from Vex.
Phase 2: Destroy the Oracles in The Vault of Glass
In this phase you just have to destroy the yellow balls of light. When you have destroyed enough you move onto the next part. If you don’t manage to destroy an oracle you will be marked and die next time the Templar does his nuke ability.
Phase 3: Defeating the Templar in The Vault of Glass
In this part a relic spawns in the middle of the room. Designate one team member to pick it up. He will have a shield while he has it equipped and it does a lot of melee damage to Vex. Picking up the relic will spawn the Templar. He shoots out purple missiles that do a lot of damage. Don’t get close to the Templar otherwise he one shots you with melee. The Templar can’t be damaged by ordinary attacks. Use the relics super ability on the Templar. This removes his shield so anyone in the fireteam can damage the Templar. Whenever that happens one of you team members might get trapped in a red globe. You need to destroy it quickly by shooting it otherwise you will die.
The guardian with the relic should kill as many of the Harpies as possible since that charges the super of the relic quicker. Note that Oracles also spawn during the fight. If you don’t kill one you will get marked and die when the Templar doe his nuke ability. If you get marked go up the the guardian with the relic and get him to cleanse you.