Skulls

Skulls can refer to a number of different topics in the Halo franchise and universe, including:
 * Skull - Human skulls are usually used in gametypes such as Oddball or Headhunter as well as being used as a collectible/game modifier in Halo 2, Halo 3, Halo Wars and Halo: Reach. The Sangheili skull is most iconic for being on the Ledgendary icon for Campaign.
 * Halo 2 Skulls - In Halo 2, skulls are collectible within the Campaign. Once collected, a skull makes gameplay either more humorous, or more challenging. This wears off after turning off the XBOX or quitting the game on Halo 2: Vista.
 * Halo 3 Skulls - In Halo 3, skulls are collectible within the Campaign. To use a skull, you must collect one then turn it on. After collection, the skull is permanently available for use. Once activated, a skull makes gameplay either more humorous, or more challenging.
 * Halo Wars Skulls - In Halo Wars, skulls are collectible within the Campaign. To use a skull, you must collect one then turn it on. After collection, the skull is permanently available for use. Once activated, a skull makes gameplay either more humorous, or more challenging.
 * Halo: Reach skulls - In Halo: Reach, all skulls are available from the beginning. They are the same as the Halo 3 Skulls. Once activated, a skull makes gameplay either more humorous, or more challenging.