Skulls are special difficulty modifiers. They are typically applied to the Weekly Strike, Daily Heroic, Hard Mode Missions, etc.

This change how the enemies act, ammo drops and damage dealt. Pay attention especially when there are more than 2 modifiers on any given mission. The more there are, the harder it's going to be.

Nightfall:

Nightfall gets special mention. It your Fireteam is all downed, you are set immediately back to orbit. This gives your whole team one shot at the mission. If you wipe, you're back to the start of it!

Modifiers[edit]

Skull Effect
Juggler No ammo drops for your Equipped Weapon. Ghost won't give you ammo when your supplies are depleted.
Anger Issues Minions of the Darkness display heightened aggression.
Angry Minions of the Darkness won't flinch, even after massive damage.
Arc Burn Arc Damage from any source is greatly increased.
Solar Burn Solar Damage from any source is greatly increased.
Void Burn Void Damage from any source is greatly increased.
Lightswitch Minions of the Darkness deal much more melee damage.
Heroic Enemies appear in greater number and are more aggressive.
Epic Heavily shield and highly aggressive enemies appear in great numbers.
Nightfall You will face a relentless army that has never known defeat. If all players die, you will be returned to Orbit.

House of Wolves Modifiers[edit]

Skull Effect
Trickle Recharge of abilities is significantly reduced.
Small Arms Primary weapon damage is favored
Airborne Players deal more damage while airborne.
Brawler Guardian Melee damage is greatly increased.
Grounded Players take more damage while airborne.
Catapult Grenade recharge is greatly increased.
Exposure Guardian shields are increased but do not replenish.
Specialist Secondary weapon damage is favored.