Mass Effect 3

Story related. If you want more info, continue reading. Otherwise, know that this will unlock through the natural progression of the story.

Mission – Priority: Cerberus Headquarters
Acquisition - Automatic after leaving Horizon.
 

This mission is the point of no return. Once you begin the mission, there’s no turning back or further exploration. This mission will be available immediately following Horizon. Other than the boss battle, it’s not too hard.

Insanity Tips:

• You are required to take EDI on this mission. Unless you are an infiltrator and have sabotage, take Tali. The hacking ability will be invaluable when it comes time to deal with the turrets.
• Worry about the atlas first. The nemesis will stay in it’s perch for as long as the fight goes on. Kill her last. With EDI, you’ll have incinerate to help take down the atlases.
• In the tunnels is where the hacking becomes vital. Combat engineers will set up numerous turrets to slow you down. Destroy the shield pylons and then hack the turrets.
• Kai Leng is an awful, awful boss battle. When you get his shields down halfway, he’ll run away to recharge them and then call down four assault troops. Get his health three quarters down and he’ll call in four assault troops and a nemesis. Again, you get his shields down to one bar and he’ll call in two phantoms. Oh, and there are no checkpoints for this part. His tactics include jumping around for no apparent reason, running away, and using a biotic sweep that wipes out your shields. Once you get his shields down, his health goes down quickly. Use when the renegade prompt pops up to finish the job.