You can earn and find Halo wars skulls by completing activities in-Game and during missions. They are all optional objectives but getting the Halo wars 2 Skulls is pretty straight forward. Every skull has a different effect and can give you bonus benefits as you play the game in harder difficulties. Plus heck out a video below that gets you the Phoenix Logs locations.
Halo Wars 2 Skulls: Locations, Benefits & Effects:
Grunt Birthday Party Skull
Mission to get Skull: A New Enemy
How to get Skull: Focus on Capturing 4 of the Decimus’ Power Nodes to earn the skull.
The Skulls effect: When killing Grunts their heads will explode with confetti
Paintball Skull
Mission to get Skull: Ascension
How to get Skull: Destroy the hidden Facility’s four Structures to earn the skull
The Skulls effect: Marine grenades & Grunt Mines splatter the environment with color (as well as deadly shrapnel)
PainTrain Skull
Mission to get Skull: Ascension
How to get Skull: Destroy the banished base Earns skull on the Island
The Skulls effect: All player units train 50 percent faster. But your Final score will be lower.
Bountiful Harvest Skull
Mission to get Skull: One Three Zero
How to get Skull: Don’t let any of your prison squads Die Protect them at all cost.
The Skulls effect: Supply from supply pads arrives 25% faster. Final score will be lower
Emperor Skull
Mission to get Skull: The Cartographer
How to get Skull: Destroy both mini
The Skulls effect: All player Powers recharge in half the time. Final score lower
Pestilence Skull
Mission to get Skull: Lights out
How to get Skull: Rescue all 10 Squads of UNSC Prisoners
The Skulls effect: All player units slowly lose health from the moment they’re built. Final score Higher!
Total Annihilation Skull
Mission to get Skull: From the Deep
How to get Skull: Mission Completed without Spartan downed
The Skulls effect: Spartan special-ability Slams create an even more powerful explosion on landing. final score lower
Sickness Skull
Mission to get Skull: Hold the Line
How to get Skull: No Barricades destroyed
The Skulls effect: All player units have 50 percent fewer hit points. Final score higher!
Firestarter Skull
Mission to get Skull: Hold the line
How to get Skull: Particle Cannon stays above 50 percent health
The Skulls effect: Grunts and Marines explode upon death, inflicting damage on enemy units. Final score lower
Things That Make You Go Boom Skull
Mission to get Skull: Under the dark
How to get Skull: All three Brute Warlords eliminated
The Skulls effect: Hero units unleash a nuclear explosion upon death. Final score lower
Wuv Woo Skull
Mission to get Skull: The Foundry
How to get Skull: Scarab survives the mission
The Skulls effect: Scarab and Locust beam weapons shoot rainbows made of pure love and hearts.
Sugar Cookies Skull
Mission to get Skull: The Foundry
How to get Skull: Scarab health doesn’t drop below 25 percent
The Skulls effect: All player units have 50 percent more hit points. Final score lower
After Party Skull
Mission to get Skull: The Halo
How to get Skull: Bravo Base is rescued
The Skulls effect: Anytime a Firebase is destroyed, the player who owned it gets a tank and infantry unit. Final score lower
Nightmare Skull
Mission to get Skull: The Last stand
How to get Skull: Control room Shield takes less than 25 percent damage
The Skulls effect: No checkpoints or saves on any difficulty. Campaign only. Final score higher
Shadow Skull
Mission to get Skull: The Last Stand
How to get Skull: Both Brute Warlords and their reinforcements eliminated
The Skulls effect: All infantry units start cloaked. Final score lower
Video of Halo Wars 2 Skull locations: