Halo 5: Guardians features a total of 13 collectible skulls that are hidden throughout its Campaign. These allow you to start up Campaign missions with a variety of effects, some of which make the game more difficult, and others simply more fun
Below are all the skulls and the effects they allow you toggle after being collected:
- Black Eye - Shields do not recharge until you melee enemies
- Blind - HUD and first-person arms/weapon hidden
- Catch - Enemies are grenade happy
- Cowbell - Acceleration from explosions increased
- Famine - Weapons drop less ammo
- Fog - Motion sensor is disabled
- Grunt Birthday Party - Head shot a grunt for a surprise
- Iron - Cannot revive/be revived
- IWHBYD - Rare combat dialog becomes more common
- Mythic - Increased enemy health
- Thunderstorm - Enemy abilities upgraded
- Tilt - Enemy resistances/weaknesses enhanced
- Tough Luck - Enemies berserk, always dive, and never flee
Mission 1 - Osiris: IWHBYD
A couple minutes into this campaign you'll be asked to transition between an outdoor, snowy environment to a large, indoor complex. Before entering, Climb on the left ledge and you'll see the black skull near the edge of the ledge which protrudes outward into space.
Mission 2 - Blue Team: Black Eye
When you enter the large Reactor Room, which has aqua colored lighting, head to the center of the room and climb the boxes. Once up top, follow the thick piping before jumping across the gap. You'll then see a vent grate below you, which you can break through with a Ground Pound or melee attack. The skull is located in the area below.
Mission 3 - Glassed: Iron
You must play on Legendary to unlock this skull. Use the scorpion to destroy the Phaeton overhead. The skull will then be available in the Scorpion garage.
Mission 5 - Unconfirmed: Blind
Upon entering the underground area, turn around and look for an opening near the entrance lighting. Climb upward, jump across the gap, and then enter the cave to locate the skull.
Mission 6 - Evacuation: Thunderstorm
Destroy the five cones and this skull will appear during the sprint to the Pelican evacuation.
Mission 7 - Reunion: Grunt Birthday Party
Early on in the mission you'll encounter your first Covenant enemies. Immediately enter the tunnel on the right side of the area. In here you'll find downed Phantom and more Covenant. Hug the right wall until you come across the Grunt who is singing on the cliff. Assassinate him by pressing X to receive the skull.
Mission 7 - Reunion: Fog
Upon seeing Cortana, you'll be asked to walk across a bridge. Instead, head right down the side path. Hug the left side upward until you find the skull at the end.
Mission 8 - Sword of Sangelios: Mythic
This skull is on top of some step-like pillars near the sinkhole as you exit the ruins.
Mission 10 - Enemy Lines: Catch
You'll find this inside the Kraken. The only way to get to it is by using a flying Banshee.
Mission 12 - Sword of Sunaion: Cowbell
Once you are in the area where the Warden appears, go into the metal structure toward the end of the street to find the skull.
Mission 13 - Genesis: Tilt
Once the Warden appears, look next to him for a rock formation. The skull is in this formation.
Mission 14 - The Breaking: Famine
At the beginning of the mission head forward to the circular area. Head left, and just to the right of the ramp go into the interior space. If you head to the middle of this room where the right and left side meet, you'll see the skull lying on the front side of the structure.
Mission 15 - Guardians: Tough Luck
When near the Gamma Core, head to the side where the structure is located. Climb up to the right side of the structure and jump toward the UNSC vehicle. The skull is next to the downed vehicle.