Outpost Tremonius Collectibles

Immediately upon exiting the elevator at the start of Outpost Tremonius, you will find the first Spartan Core directly in front of you. This core can be used to upgrade your Mjolnir Suit Upgrade or your Grappleshot and unlocks the Hidden Experience achievement.

After collecting the first Spartan Core, proceed through the rooms and eliminate the Grunts in the hallway. Interact with the terminal in the next room to trigger a cutscene (a non-interactive cinematic the game plays automatically) where Escharum speaks to Master Chief. Upon completion, you will unlock the Zeta achievement. Your objective is to clear the outpost for Echo 216 to land.

Before engaging enemies outside, turn right from your starting position and go behind the structure you exited. Here you will find the second Spartan Core on the ground next to a weapon crate.

To the left of where you found the second Spartan Core, head up the hill. In a cave, you can find an Energy Sword by defeating an Elite Brute wielding it and possessing Active Camo. This is a difficult fight; eliminate the sleeping Grunts outside first, then use grenades to lure the Brute out. Use your highest damage weapon and melee attacks, but use the Grappleshot to escape if necessary. You can also find a Heatwave in the room where the Elite Brute was triggered.

After defeating the Elite Brute and collecting the second Spartan Core, enter the main outpost area. To the left of where you first entered, down the hill, you will find the third Spartan Core. Next to it are M41 SPNKR and S7 Sniper Rifle power weapons.

Use the M41 SPNKR or S7 Sniper Rifle to shoot explosive coils on the ledge above to eliminate the Grunts there, including the one operating the plasma cannon. You may need to clear ground enemies first. A Stalker Rifle can be found in the outpost buildings if you cannot access the power weapons beforehand.

Once the enemies on the ground and ledge are cleared, look beneath the landing platform. To its right, you will find a Banished audio log surrounded by cargo. This can be collected later if missed.

At the top of the hill near the landing platform, you will find the Mjolnir Armor Locker. Before reaching it, you must defeat Banished reinforcements dropping from a 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 landing platform; use them or throw grenades to weaken enemies. Avoid close combat with Elite Brutes on the platform and use ranged attacks and cover (press the cover button to crouch behind walls or objects).