The first skull of the game, 'Blind' can be found after the first fight in Sierra 117, at the far end of the area. One skull in this game will require the game to have been completed previously on at least Normal difficulty, so it's best to save these collectibles until your second playthrough. Skulls will not spawn if you play on Easy or if you start the mission from a later rally point. In order to collect them, you must start each level from the beginning on at least Normal difficulty. There are a total of 13 skulls scattered throughout the campaign. PREVIOUS: Halo 2: Anniversary - Skull Location Guide Campaign Skulls There was also a limited time 'Acrophobia' skull that could be unlocked by killing 343 flying enemies in the campaign, though that deadline has since expired. The multiplayer skulls do not have any affect other than to give you that sweet, sweet gamerscore, but they will be detailed here as well. The campaign skulls are traditional skulls that can be 'activated' and affect gameplay, both for better and worse.

Halo 3 has 19 skulls total, with 13 in the campaign and six in multiplayer maps. Halo 2 featured skulls, but didn't add it's terminals or dolls until the anniversary release, and Halo: CE didn't have collectibles of any sort until 2011. Halo 3 was the first game in the franchise to really go all-in on the collectibles, featuring skulls in both the campaign and multiplayer, as well as terminals spread throughout the campaign.

Halo 4 skulls