Modifications are items in Horizon Zero Dawn and Horizon Forbidden West that can be added to Aloy's equipment to increase stats and perks. Coils are modifications applied to weapons and weaves are applied to outfits.

They can first be used upon completion of the main quest, Lessons of the Wild, with the exception of Spear Damage Coil, added by The Frozen Wilds, which first requires the side quest, A Secret Shared, to be completed. They can be obtained from Treasure Boxes and looting machines.

Modifications come in three types: Common, Rare and Very Rare with the amount of increase in the given stat depending on the rarity. Some modifications can provide a boost to more than one stat at a time.

Forbidden West introduces a fourth type, legendary; these often have unique effects compared to lower tier modifications. Many modifications can also now be purchased from specific merchants in limited quantities.

Modifications in Horizon Zero Dawn

Coils

Coils are modifications that can be added to weapons to increase damage dealt or handling stats.

• Corruption Coil (Elemental)
• Fire Coil (Elemental)
• Freeze Coil (Elemental)
• Shock Coil (Elemental)
• Damage Coil
• Tear Coil
• Handling Coil
• Spear Damage Coil

In the base game, the minimum modification value for all weapons coils is 6% and the maximum value varies depending on the effect and its "rank" on the mod:

• Elemental damage bonuses have a maximum value of 50% when it is the primary effect and a maximum value of 17% when it is the tertiary effect. Elemental damage bonuses can not be rolled as a secondary effect.
• Damage and Tear bonuses have a maximum value of 50% when it is the primary effect and a maximum value of 25% when it is the secondary effect. These bonuses can not be rolled as a tertiary effect.
• Handling bonus has a maximum value of 67% if it is the primary effect (=Handling Coil) or a maximum value of 33% if it is the secondary effect. It can not be rolled as a tertiary effect.
• Spear Damage Coil always provides a single damage bonus effect with a maximum value of 30%.

Important notes:

1. Secondary effect can only be Damage, Tear or Handling bonuses
2. Tertiary effect can only be an Elemental damage bonus.
3. A coil can not have two bonuses with the same effects

Weapon coils can only be used to augment a weapon's existing abilities and not add new ones. For example, Fire Coils cannot be added to the Sharpshot Bow because it cannot deal any Fire damage. If a coil provides more than one benefit, the primary effect will determine what weapons it can be applied to. This means that coils with multiple effects can sometimes be added to weapons that will not benefit from the secondary and/or tertiary benefits.

Weapon	Compatible Modifications
Hunter Bow	Damage, Tear, Fire, Handling
Sharpshot Bow	Damage, Tear, Handling
War Bow	Freeze, Shock, Corruption, Handling
Tripcaster	Damage, Fire, Shock, Handling
Ropecaster	Damage, Tear, Handling
Sling	Fire, Freeze, Shock, Damage, Handling
Blast Sling	Damage, Handling
Rattler	Damage, Tear, Freeze, Shock, Handling
Stormslinger	Shock, Handling
Icerail	Damage, Freeze, Handling
Forgefire	Damage, Fire, Handling

Weaves

Weaves are modifications that can be added to outfits to increase resistance to different types of damage or increase stealth stats.

• Resist Corruption Weave (Elemental)
• Resist Fire Damage Weave (Elemental)
• Resist Freeze Damage Weave (Elemental)
• Resist Shock Damage Weave (Elemental)
• Resist Melee Damage Weave (Physical)
• Resist Ranged Damage Weave (Physical)
• Stealth Weave

In the base game, the minimum modification value for all outfit weaves is 6% and the maximum value varies depending on the weave's effect and its "rank" on the mod:

• Elemental resistance weaves have a maximum value of 33% when it is the primary effect, a maximum value of 17% when it is the secondary effect and a maximum value of 12% when it is the tertiary effect.
• Ranged and Melee (Physical) resistance weaves have a maximum value of 20% when it is the primary effect, a maximum value of 10% when it is the secondary effect and a maximum value of 7% when it is the tertiary effect. 
• Stealth weave has a maximum value of 15% when it is the primary effect, a maximum value of 7% when it is the secondary effect and a maximum value of 5% when it is the tertiary effect.

Important notes:

1. Secondary effect can either be the opposite effect type of the primary bonus (Elemental <> Physical) or be a stealth bonus
2. Tertiary effect is always matching the primary effect type or is a stealth bonus.
3. A weave can not have two bonuses with the same effects

Unlike weapons coils, outfit weaves can add new abilities to outfits and are not bound by the defense already provided. For example, although the Nora Protector outfit does not provide Fire resistance, a Resist Fire Damage weave can be applied to add that ability.

Unique Modifications

The Frozen Wilds DLC adds eleven unique modifications to the game which are found in fixed locations. Once obtained, they can be dropped, dismantled by using a bug, but can not be sold.

Each one counts for ⁸⁄₁₁% (≈0.73%) Frozen Wilds game completion.

Unique Weapon Coils

Icon	Name	Effects	Location	Optimal Weapon
	Drummer's Weapon Coil	+51% Freeze +35% Shock +35% Corruption	At the very bottom of Greycatch after draining all the water	War Bow
	Hidebound Weapon Coil	+51% Damage +35% Shock +35% Freeze	Reward for delivering Animal Figurine 3 to Enjuk	Rattler
	Painted Weapon Coil	+51% Shock +35% Fire +47% Handling	Reward for delivering Oxide Pigments to Sekuli	Tripcaster Secondary*: Sling
	Pristine Weapon Coil	+51% Damage +35% Tear +47% Handling	Reward for completing the errand Out of the Forge	Sharpshot Bow Secondary*: Hunter Bow, Rattler
	Untested Weapon Coil	+51% Damage +35% Tear +35% Fire	Reward for completing the side quest The Hunters Three	Hunter Bow
	Veteran's Weapon Coil	+51% Fire +35% Shock +35% Freeze	Reward for getting all golds on Snowchants Hunting Grounds	Sling

*: Secondary weapons make use of all the mod's attributes, but the mod itself lacks at least one of the elemental types of the weapon. The painted weapon coil lacks freeze for the sling, while the pristine weapon coil lacks shock and freeze for the rattler, as well as fire for the hunter bow.

Unique Outfit Weaves

Icon	Name	Effects	Location
	Heat Sink Outfit Weave	+34% Resist Fire +20% Resist ranged attacks	About halfway through the Firebreak Facility - in the the large room where Aratak and Ourea propose alternative routes, this weave is on "Aratak's route", with the remains of the previous expedition.
	Insulated Outfit Weave	+25% Resist Shock +25% Resist Freeze +25% Resist Fire	In a supply crate next to the control tower in the far northeast of the Cut.[1]
	Reinforced Outfit Weave	+20% Resist ranged attacks +34% Resist Freeze	About halfway through the cave system along the Shaman's Path
	Survivor's Outfit Weave	+34% Resist Freeze +20% Resist Melee attacks	Reward for getting gold on Ikrie's Challenge
	Warrior's Outfit Weave	+20% Resist Melee attacks +34% Resist Fire	In a supply crate at the Banuk fishing camp southwest of Deep Din

Modifications in Horizon Forbidden West

Coils

Coils are modifications that can be added to weapons to increase damage dealt, handling stats, status chance, or add context dependent damage.

Icon	Name	Effects	Location	Optimal Weapon
center|50x50px	Instant Brittle Chance	Has a %3 to instantly brittle a foe on hit.	Bought from Dukkah.	Boltblaster
center|50x50px	Instant Burning Chance	Has a %4 to instantly burn a foe on hit.	Bought from Dukkah.	Boltblaster
center|50x50px	Instant Explosion Chance	Unknown. Needs expirimentation.	Bought from Dukkah.	Boltblaster
center|50x50px	Instant Plasma Chance	Has a %4 to instantly inflict Plasma hit.	Bought from Dukkah.	Boltblaster

References

1. ↑ Due to a bug, it may only appear during the Frozen Wilds errand, The Claws Beneath.