There are 15 skulls to collect in Halo Wars, that will either enhance gameplay or change it. Have fun!
Skulls 1-8 locations coming soon
Skulls and what they do

Look Daddy!- Grunts' methane tank explodes on death
Grunt B-Day- Grunts explode into confetti
Cowbell- Destruction physics magnification enhanced 2 times
Wuv Woo- Scarabs fire rainbow beams of pure love
Fog- no minimap
Sickness- All player units explode into flood units on death
Rebel Sympathizer- Nonplayer units receive +25 percent more HP
Rebel Supporter- Nonplayer units inflict +50 percent more damage