Skull Name: Boomstick (Mission 12: Repairs) - Kill 12 Spirit Transports - take a Hawk to the Lower 2 Airlocks and it its right up the Little ramp in the Air
Skull Name: Bountiful Harvest (Mission 14: Reactor) - Kill 20 Vampires - head to the Second Covenant Base and its in the Far corner at the bottom of the next ramp
Skull Name: Catch (Mission 10: Shield World) - Kill 350 Swarms - get at least 2 Hornets and fly East of you base past the First Tower to a Plateau with covered with Flood Eggs it is in the center
Skull Name: Cowbell (Mission 3: Relic Interior) - Kill 45 Hunters - take a Grizzly, Anders, Forge and Your Marines Back to where they were held up on the central pad
Skull Name: Emperor (Mission 15: Escape) - Kill 3 Scarabs - Head the to Very North of the Map and its dead Center of all the flood
Skull Name: Fog (Mission 5: Arcadia Outskirts) - Kill 5 Wraiths - get a Warthog and rush back up the Tracks to the left of your Main Base and just keep going straight past the split in the Tracks
Skull Name: Grunt Birthday Party (Mission 2: Relic Approach) - Kill 20 Jackals - head back to Alpha Base with a Worthog its in the south end of the base
Skull Name: Look Daddy! (Mission 1: Alpha Base) - Kill 100 Grunts - get a Warthog and rush back to the front gate of Alpha base the skull is where the Marines were held up
Skull Name: Pain Train (Mission 13: Beachhead) - Kill 10 Bomber Forms - head back to the Beginning of the Map by the First Teleporter and head down the Path to a Flood nest and its right next to it
Skull Name: Rebel Leader (Mission 9: The Flood) - Kill 20 Flood Stalks - just to the North East of your Main Base is a downed Pelican. Just take a Warthog to claim it fast and easy
Skull Name: Rebel Supporter (Mission 8: Anders' Signal) - Kill 750 Infection Forms - head to North Side of the Map where you got the Elephant, head east towards a cliff, But you'll see a ridge. Go into ridge
Skull Name: Rebel Sympathizer (Mission 7: Scarab ) - Kill 10 Locusts - get a Warthog and take it to the Top Left of the Map where there was 2 Locusts and a Power Nod its right there
Skull Name: Sickness (Mission 6: Dome of Light) - Kill 50 Banshees - take a Squad of Marines to the Hanger Behind your Base its right there
Skull Name: Sugar Cookies (Mission 11: Cleansing) - Kill 100 Sentinels - take a Hornet to the front end of the Spirit Of Fire and it is right on the nose of the Ship
Skull Name: Wuv Woo (Mission 4: Arcadia City) - Kill 50 Elites - where you Set up Base Two in the Streets there are some stairs Next to it leading to a Bronze Statue Its next to the Statue