I Thought I'd Lost You
From Halopedia, the Halo wiki
I Thought I'd Lost You is an achievement in Halo 5: Guardians, awarded for escaping the Hunters in the lab and fighting them in the hangar in Blue Team. The achievement artwork is concept artwork of Frederic-104.
As soon as the player takes the elevator to the laboratory, they must immediately run to the tube that leads to the reactor room. Blue Team will then fight four Hunters instead of two in the Prowler's hangar bay at the end of the mission. On higher difficulties, escaping from the Hunters in the lab is more difficult as they can more easily take down the Blue Team members. For this reason, when attempting this achievement on higher difficulties, it is recommended to take the lab equipment as per Fred's recommendation (when he says "Use the lab equipment to keep above them and out of reach.") to stay above the Hunters and avoid their projectiles. Having an Energy Sword equipped is also useful due to the boost it gives to the player's movement speed.