Horizon Forbidden West is filled with many great characters that help Aloy on her journey. Some of these people come from interesting backgrounds that you might not expect to lend their help on the trip. Kotallo is a high-ranking Tanakth member who shows he has a lot more to him than a suspected savage man in the west. Here is how to complete his side quest, What Was Lost.
You will be able to begin the What Was Lost side quest after you have retrieved the three pieces of Gaia. At that point, you can talk to Kotallo in the base (or at Memorial Grove if you have completed the story). He will tell you how Gaia told him about a way to build a new arm and wishes to have your help. When you are ready, go to the marked campfire and call him.
Step one
For this mission, you need to enter the old research facility that you found Beta in earlier in the story. When you arrive, you can fight all of the machines on your way to that room, or you can just run past them. When you get to the room, interact with the console on the far end of the room.
After you have the schematics to build the arm, some Spectors will arrive and attack you. Kill them, and you will be directed to the second floor of the facility to find the components for the arm. When you arrive in the lab you need to be in, look up at the ceiling and pull down the vent.
Climb up and over into the next room to find the components in a chest you have to pry open. Return to Kotallo to finish this first step.
Step two
When you are ready to continue the side quest, return to Kotallo, and he will tell you he wants to test the new arm. Meet him near the area where you both took down the Tremortusk earlier, and he will lead you to a Scorcher. All you need to do is kill the Scorcher for Kotallo to decide he doesn’t need to wear the arm at all times. Just like that, the side quest is over.
