HaloRadar: Guide to Every Skull

Above: You know you want them...

When searching for skulls, start missions from the beginning on Normal or higher difficulty.
To enable a skull's effect, choose Campaign in the main menu and then hit "X" to bring up the Edit Menu.

Gold Skulls

These make the game more brutal.

Iron
Black Eye
Tough Luck
Catch
Fog
Famine
Thunderstorm
Tilt
Mythic

These make the game more fun.

Blind
Grunt Birthday Party
Cowbell
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