Look Daddy
Kill 100 Grunts. In Mission 1 (Alpha Base), the Skull can be found on the left side of the last battle area before you go into Alpha Base. When Grunts die, their methane tank will always shoot off.
Grunt Birthday Party
Kill 20 Jackals. In Mission 2 (Relic Approach), the Skull can be found on the south edge of Alpha Base, just inside the walls of the base. Grunts explode into confetti when killed.
Cowbell
Kill 45 Hunters In Mission 3 (Relic Interior), the Skull can be found at the very back in a circular platform where you have to save Forge/Anders. Destruction physics are increased.
Wuv Woo
Kill 50 Elites. In Mission 4 (Arcadia City), the Skull can be found on the right side of the map just below the Covenant base. It is just past the top of the stairs. Scarabs shoot rainbows.
Fog
Kill 5 Wraiths. In Mission 5 (Arcadia Outskirts), the Skull can be found on the left side of the map, at the top left corner. The mini-map is disabled, and your final score will increase.
Sickness
Kill 50 Banshees. In Mission 6 (Dome Of Light), the Skull can be found just inside the big hangar behind your base. All player units have 50% fewer hit points, and your final score will increase.
Rebel Sympathizer
Kill 10 Locusts. In Mission 7 (Scarab), the Skull can be found on the left side of the map at the very edge of the battlefield area. There is a ledge that projects over the canyon, next to a Power Node. Non-player units get 25% more hit points, and your final score will increase.
Rebel Supporter
Kill 750 Infection Forms. In Mission 8 (Anders' Signal), the Skull can be found to the far right of where Echo gets taken over by Flood on the ridge. Non-player units do 50% more damage, and your final score will increase.
Rebel Leader
Kill 20 Flood Stalks. In Mission 9 (The Flood), the Skull can be found very close to the base on top of a plateau (near the burning Covenant ship). Non-player units start with extra veterancy, and your final score will increase.
Catch
Kill 350 Swarms. In Mission 10 (Shield World), the Skull can be found on an island located to the southeast. A flying unit is required to retrieve it. All player units recharge unit abilities in half the usual time, and your final score will be decreased.
Sugar Cookies
Kill 100 Sentinels. In Mission 11 (Cleansing), the Skull can be found floating in front of the ship. A flying unit is required to retrieve it. All player units have 50% more hit points, and final sore will be decreased.
Boomstick
Kill 12 Spirit Transports. In Mission 12 (Repairs), the Skull can be found on the super structure on the Spirit of Fire at the far end from the Power Core. A flying unit is required to get above the main deck on a platform in order to retrieve it. There will be a 5% chance any non-player unit blows up upon death, with explosive area of effect damage, and your final score will decrease.
Pain Train
Kill 10 Bomber Forms. In Mission 13 (Beachhead), the Skull can be found on a Flood vent, where the Flood appear from as you try to enter the Pelican. All player units train 50% faster, and your final score will decreased.
Bountiful Harvest
Kill 20 Vampires. In Mission 14 (Reactor), the Skull can be found just behind and to the left of the second Covenant base. Supplies come in 25% faster, and your final score will be decreased.
Emperor
Kill 3 Scarabs. In Mission 15 (Escape), the Skull can be found directly behind the Flood base, at the very rear of the map. It is pinpointed to the northeast when looking at the mini-map. All player powers recharge in half the time, and your final score will be decreased.
Source: www.cheatcc.com
