Item Durability

Using the same tools over the course of days or weeks or months or years, it will eventually begin to see imperfections appear. Same goes for weapons and armor. Steel doesn't cut steel, it dents itself and scrapes and damages at a molecular level and potentially becoming visible damage. In some cases this can become dangerous depending on the dent size and location or the integrity of the object being hit.

• Whenever you critically fail an attack roll that involves a weapon attack the weapon takes a -1 to attack and damage rolls.
• A basic +0 weapon can take up to a -3 durability before breaking. +1/2/3/4/+ weapons increase this break threshold by the + to hit of the weapon on a 1:1 ratio.
• Once a magical weapon breaks its magical threshold and enters the +0 threshold, the magic of the item fades, requiring the item to be brought to an arcane Smith to reinfuse the magic. The weapon's damage is still considered magical, until it breaks.

Example: A normal Shortsword can take a total of -3 durability before breaking. A Shortsword +1 can take -4 durability before breaking, and so on.

• Picking any weapon off the ground, whether it is from looting a dead body, or digging it out of a treasure pile will start that weapon off with a 50% chance to already have a damaged durability at a -1d2 damage.
• A broken weapon can be used in combat, as a blunt sword to the head will still hurt, but a "Broken" weapons attack rolls are made at disadvantage.

Example: You kill an orc and pick up his hand axe. You or the DM rolls a d%. On a 00-49 the weapon is undamaged. On a 50-100 roll a d2, this is how much starting damage the weapon has to durability.

Armor Degradation

Wearing the same set of armor for even a couple days of serious, continued battle will see the armor loose its protective qualities. Steel can't cut through steel, but it sure can dent and damage itself with enough force.

• Whenever you are critically hit by a weapon or spell attack, or critically fail a DC your equipped armor takes -1 point of damage.
• Armor breaks when it reaches less than your natural armor value (10 + Dexterity Bonus).

Example: Leather armor can take a total of -1 damage before breaking because its calculated 11 + Dexterity. Meaning that when it takes -1 damage, it is no better than being unarmored.
Example: Say your Natural Armor is 12 (10 + 2). Plate armor, with an AC of 18, can take -6 damage before it breaks.

Acid Damage

It sizzles! It burns!

• Acid! Acid hurts! Any person in armor that ends their turn in a pool of acid takes -2 armor degradation and -1 weapon degradation instantly.

Dragons Breath

The heat of a red dragon's fire or the cold of a black dragons acid. All of them hurt.

• Being hit by a Breath Attack requires a successful save to usually take half damage. If successful weapons are probably fine! But your armor takes a -1 to durability. If you fail the save and take the full force of the attack then your armor takes -2 durability.
• Acid Breath attacks follow the success rules but the values are doubled. A successful save degrades armor by -2. A failure against an Acid breath attack is quite harmful dealing -5 damage.

Weapon and Armor Repair

When a piece of gear finally breaks it will need to be brought to a Smith capable of repairs.

• You can use a whetstone to sharpen a non broken weapon to give it a temporary +1 for the next 8 hours. This time reduces by 2½ hours for every combat encounter the sharpened weapon sees. Magical weapons cannot be sharpened, unless they have hit the +0 threshold.
• You can use armor polish to polish or oil a non broken set of armor to give it a temporary +1 for the next 12 hours. This time reduces by 4 hours for every combat encounter the polished armor sees. Magical armor cannot be polished. Masterwork armor can be polished back to its +1 state but only temporarily when armor polish is used.
• With the proper tools, materials, time, and knowledge of the Occupational Skill: Smithy, you can attempt to repair gear on your own. The DC is 12 + 1 for every point of damage acquired by the item.

Masterwork Gear

Masterwork gear is personalized gear that only you or someone of your near exact dimensions can effectively use. Masterwork weapons are balanced and made to fit the wielder best, and Masterwork armor is fitted and tightened to best fit the body it was made for.

• The +1 that is gained from masterwork functions just like a magic item +1 for calculating how much damage an item can take.
• Repairing a masterwork item back to +1 takes more money and skill than it does time. Not every Smith can make masterwork armor, and even less can repair it.

Mythril Gear

A light and strong metal!

• Mythril gear can only be damaged on critical hits if the weapon attack is magical.

Adamantite Gear

The strongest metal!

• Adamantite gear can only be damaged by Acid attacks that critical hit or you critical fail a save against.
• Adamantite gear can only be damaged by Dragons Breath attacks that fully connect. Some weapons are forged with the fury of some dragons after death. These dragon infused weapons deal damage to Adamantine gear on critical hits. These weapons are usually pretty easy to see as they contain large parts of the dragon. These weapons follow the weapon rules of Adamantine Weapons for losing durability.
• Adamantite weapons do not dull or blunt on critical fails.

Dragon Gear

• Dragon gear can only be damaged on critical hits if the weapon attack is magical.
• Dragon gear negates damage taken by the dragon breath attack of the same type. 

Example: Red Banded Dragon Hide (made from wyrmling-young adult red dragon scales) resists the damage the armor would take from a Red Dragons breath attack.

Legendary Quality Gear and Artifacts

• Most legendary quality items and Artifacts quality items cannot be damaged in these ways. These items usually require very specific circumstances to even damage the item, and even more exact circumstances to destroy the item.

The Mending Cantrip

A cantrip used by explorers and researchers alike to prevent the destruction of great knowledge.

• Mending can be used to bring a broken weapon from -3 to a -2 but cannot repair a weapon further.
• Mending can be used on a broken armor set to give it +1d2 durability, but cannot repair armor further.

The Repair Spell

A spell of a lost empire that has been preserved by the gnomes and elves of the world.

• Using the repair spell one can fix -1 damage occurred on a weapon or armor back to +0
• This can fully repair masterwork armor and weapons back to a +1 state, but cannot repair the magics of a +1/2/3/4/+ magical item.