Skulls are the rarest collectibles in Halo 5: Guardians. Most missions feature one or two Skulls, and each Skull lets you alter your Campaign experience in a variety of ways. Here's a look at two of the Skulls you can collect.
M1: Osiris Skull—IWHBYD
This Skull makes all uncommon dialogue more common, while common dialogue becomes rarely heard.
M8: Swords of Sanghelios Skull—Mythic
This Skull doubles the health of all enemies, letting them sustain far more damage before falling.
The Halo 5: Guardians eGuide includes videos and locations of all 13 Skulls, plus the complete Campaign walkthrough and expert multiplayer strategies.