Skull unlockables/modifiers return to halo 5
Skull Menu
Skulls confirmed so far
Black Eye - Shields do not recharge until you melee enemiesBlind - HUD and first-person arms/weapon hiddenCatch - Enemies are grenade happyCowbell - Acceleration from explosions increasedFamine - Weapons drop less ammoFog - Motion sensor is disabledGrunt Birthday Party - Head shot a grunt for a surprise
Iron - Cannot revive/be revivedIWHBYD - Rare combat dialog becomes more commonMythic - Increased enemy health
Tough Luck - Enemies berserk, always dive, and never fleeThunderstorm - Enemy abilities upgradedTilt - Enemy resistances/weaknesses enhanced
Find before you can Use gameplay *spoilers*
sources: ign and reddit