Halo: Campaign Evolved features a substantial collection of 39 skulls to discover, each offering unique modifiers that can dramatically alter gameplay. Finding the first three skulls also automatically unlocks three additional skulls for use in the Campaign Remix mode: Armistice, Adaptation, and Reload. These skulls introduce gameplay changes like randomized enemy factions and weapon placements. Players will need to explore meticulously, as some skulls require higher difficulties, the use of other skulls, or advanced maneuvers like grenade jumps.

Pillar of Autumn Skulls

On the Pillar of Autumn, players can find three skulls. "Speed Limit," which disables sprint, is located immediately after exiting the cryo pod, on a raised platform to the right. "Magnified," which grants the Assault Rifle 60-round magazines, is found in a room with weapon racks after the bridge encounter. The "Perspective" skull, which switches the player camera to third-person, is located in the bridge cockpit, below the pilots.

Halo Skulls

The mission "Halo" offers three skulls. "Grunt Funeral," causing Grunts to explode in plasma upon death, is situated atop a Forerunner structure after exiting the underground section. "Give and Take," which drains shields on firing but recharges them by dealing damage, can be found in a cave by following the river. "Floor is Lava," inflicting continuous damage when touching the ground, is located on a large central rock near the crash site.

Truth and Reconciliation Skulls

Within the "Truth and Reconciliation" mission, players can find "Iron," which resets players to their last checkpoint upon death in co-op or restarts the level in solo. This skull is located on a lower ledge by the cliff edge near a grav lift. The "Endurance Spec" skull, making UNSC vehicles indestructible, is in the hangar on the upper level, requiring precise jumps to reach. "Foreign," which prevents players from using non-UNSC weapons, is found in a hangar after a Covenant drop ship departs; players must enter a newly opened door in the far right corner.

Silent Cartographer Skulls

The "Silent Cartographer" mission holds three skulls. "Bandana," granting infinite ammo and grenades while disabling some achievements, is inside a cave to the right of the Forerunner structure's entrance. "Acrophobia," which grants limited flight capabilities, is found at the far end of a sloping structure in the central plaza. "Hip Fire," disabling all weapon zoom functionality, is located below a staircase with a hologram in the main facility.

Assault on the Control Room Skulls

"Assault on the Control Room" features three skulls. The "IWHBYD" skull, affecting dialogue, is found in a cave halfway up an icy wall, accessible by using the Scorpion tank. "Angry," making enemies fire faster and more frequently, is located on the third strut of a Forerunner ravine structure near the Control Center Ziggurat entrance. "Cowbell," reducing the physics mass of objects, can be found in a channel on the left side of a bridge above the Forerunner structure.

343 Guilty Spark Skulls

In "343 Guilty Spark," the "Fog" skull disables the motion tracker and is found on a rock overlooking a fallen tree. The "That's Just... Wrong" skull drops from a marine who attacks the player. The "They Come Back" skull, which makes Flood Combat Forms more dangerous, is located on a rock to the left of a fallen tree near the evacuation tower.

The Library Skulls

"The Library" mission contains three skulls. "Tilt," which enhances damage multipliers, is at the top of a sloping strut next to a door after a short tunnel. "Pop," causing Flood to explode when shot in weak points, is located on a pedestal behind the door Guilty Spark is unlocking. "Famine," which reduces enemy weapon ammo, is found in a small alcove at the start of the fourth section.

Two Betrayals Skulls

For "Two Betrayals," "Tough Luck," which causes enemies to go berserk, is found at the top of a large crest structure accessible via Banshee. The "Black Eye" skull, requiring melee hits to recharge shields, is located on a pile of snow amidst Flood growths in the valley. "Mythic," increasing enemy health and unlocking LASO mode, is found in a central pillarlike structure after completing a series of combat encounters and activating terminals.

Keyes Skulls

The "Keyes" mission features three challenging skulls. "Catch," which makes enemies throw more grenades, must be acquired on Heroic difficulty from a timed grav lift. "Blind," which removes the HUD and weapons from the screen, is found in a corridor after boarding the ship and clearing a bay filled with vehicles. "Pinata," causing enemies to drop inert grenades when punched, is obtained by meleeing the Flood growth containing Captain Keyes.

The Maw Skulls

In "The Maw," "Stowed Reload," allowing weapons to reload while stowed, is on top of a pillar in a cryo pod bay. "Boom," increasing explosion radius, is found by navigating complex platforms in the engine bay. "Thunderstorm," upgrading enemy ranks, is located on the ground within a vent shortcut during the final Warthog escape.

Boarding Action Skulls

"Boarding Action" includes three skulls. "Malfunction," causing random HUD elements to disappear on respawn, is found on the ground overlooking the initial dropship room after meeting Johnson. "Johnny Ammo Seed," where reloading discards remaining ammo, is located on a walkway in the third level of a white and gold room. "Leadhead," disabling headshot damage bonuses, is found by heading through a door on the left side of a room with a grav lift after meeting the Prophet.

The Most Dangerous Game Skulls

"The Most Dangerous Game" mission contains three skulls. "Temperamental," making allies attack faster if the player kills a friendly, requires breaking a golden Elite's shield three times throughout the level. "Recession," doubling ammo expenditure per shot, is found inside a room revealed by blowing up fuel barrels. "Ghost," where enemies no longer flinch, is located on a cliff above a gravity bridge.

Heavy Burden Skulls

Lastly, "Heavy Burden" offers three skulls. "Eyepatch," disabling all auto-aim, is located on a smaller bridge off to the left after a chasm. "Grunt Birthday Party," which causes Grunt headshots to trigger celebratory effects, is on top of a rock-like structure after descending from the ship's bridge. "Efficient," causing enemies to drop more ammo when the player is at full health, must be grabbed from the far left corner of a room before a timeout countdown expires.