Outpost Tremonius

Exit the elevator and immediately collect the first Spartan Core directly in front of you. This allows you to upgrade your Mjolnir Suit Upgrade or Grappleshot and unlocks the Hidden Experience achievement.

Proceed through the next rooms, eliminating sleeping Grunts to prevent them from attacking later.

Interact with the terminal in the following room to trigger a cutscene (a non-interactive cinematic the game plays automatically) where Escharum speaks.

After the cutscene, you will be outside Outpost Tremonius. You will unlock the Zeta achievement. Your objective is to clear the outpost of all enemies for Echo 216's safe landing.

Turn right from the elevator exit and go behind the structure to find the second Spartan Core on the ground next to a weapon crate.

Optional: Head up the hill to the left of the second Spartan Core. Defeat the Elite Brute wielding an Energy Sword and using Active Camo inside the cave to obtain the sword. Take out sleeping Grunts outside the cave first, then use grenades to lure the Brute out. Use your highest damage weapon and melee attacks, but use the Grappleshot to escape its melee range if necessary. A Heatwave can also be found in this room.

Enter the main outpost area and eliminate all enemies. You can find powerful weapons like the M41 SPNKR and S7 Sniper Rifle next to the third Spartan Core, located down the hill to the left of your entry point. A Stalker Rifle is available in the buildings if you miss these.

Use the M41 SPNKR or S7 Sniper Rifle to shoot the explosive coils on the ledge above to kill the Grunts and the plasma cannon operator. Clear ground enemies first to avoid being attacked from the side or rear.

Locate the Banished audio log to the right, directly beneath the landing platform, surrounded by cargo.

Head towards the landing platform. Defeat Banished reinforcements arriving by ship and emerging from a crack in the wall. Use grenades or nearby blast coils to damage them. More blast coils are in the center of the platform. Be cautious of Elite Brutes on the platform and use ranged attacks and cover (press the cover button to crouch behind walls or objects).

The last collectible, the Mjolnir Armor Locker, is at the top of the hill near the landing platform.