New Action: Sunder

The normal wear and tear of an item is covered in its usual repair costs, but sometimes a foe will target a weapon or piece of armor to damage it more severely.
You can perform a Sunder as an attack action. If you can make multiple attacks, you may exchange one of your attacks for a sunder.

You target a worn or carried item. The item has its owner’s armor class. If you hit the item, the item suffers a 1 point of sunder damage. A weapon with at least 1 point of sunder damage suffers a -1 penalty to attack and damage rolls or a -1 to granted armor class (cannot go below +1) if it is a shield or suit of armor.
If the item reaches 5 points of sunder damage, the item becomes broken and must be repaired. The item can no longer function for its purposes. The DM may rule that certain items require less or more penalty based on the item in question.

A magic item can withstand up to an additional 2 additional points of sunder damage per level of enhancement (minimal of an additional 2 points of sunder damage for items without an enhancement bonus); magic items can only be sundered by an attack with an equivalent or greater enhancement bonus.

Some monsters may have abilities that increase the amount of damage they do to a weapon when they sunder it. The DM may rule that certain weapons are better or worse at sundering, usually in the form of advantage or disadvantage related to the sundering check.

This action was modified from the Black Pudding’s corrosive quality.

Repairing a sundered Item
Repairing an item costs 20% of its base price per point of damage to a maximum of 80% of the base price. An item that is broken still only costs 80% to repair. Repairing a magic item is difficult. You must find a blacksmith/fletcher/etc. of the race that created the item (or someone skilled in that race’s crafting technique as per the item) who has the talent for repairing magic items as well as the formula for making that item.

NOTE: Originally part of the New Actions: Block, Defense Roll, & Parry thread but has been separated to its own category.

EDIT: Changed the language from a penalty to the weapon to sunder damage.

After looking over this rule, I think the amount of sunder damage needs to be altered. This page of Roll20 details the armor class and hit points of objects.

Based on this, a sundering attack should have to puncture a different armor class than your opponent’s armor class and the threshold should be different for the item to break. I don’t like the idea of tracking individual hit point pools for items, especially if we allow them to vary based on the dice rolls (or taking the averages), so I opted for a simpler approach by reducing item health to an easily discernible flat number and the damage to that item as a flat number, modified by one or more options. I think a good replacement to the previous version of Sunder would be the following.

The Action

You perform the Sunder attack as a single attack during the Attack action. Make an attack roll versus the held, worn, or carried object’s wielder’s armor class. A successful sunder attack deals 1 point of sundering damage.

Weapon Adjustments

A weapon with the sundering quality deals an additional 1 point of damage. A slashing weapon deals and additional 1 sundering damage to cloth, paper, rope, and bone. A bludgeoning weapon deals an additional 1 point of sundering damage to crystal, stone, iron, and steel.

Material Adjustments

Objects’ sundering threshold is one point less when made of paper, cloth, rope, glass or ice. Objects’ sundering threshold is one point higher higher when made of iron or steel. Objects’ sundering threshold is is two points higher when made of mithral. Objects’ sundering threshold is three points higher when made of adamantine.

Damage Adjustments

Magical objects have a minimal two point higher sunder threshold. Objects with a +2 enhancement have a four point higher sunder threshold. Objects with a +3 enhancement bonus have a six point higher sunder threshold. Magical objects can only be sundered by a magical object of equal or greater enhancement bonus. Magical weapons deal an additional 1 point of sundering damage.

Here are the adjusted Armor Class values.

Object Armor Class when Sundering
Substance AC
Cloth, paper, rope The higher value of 10 + Wielder's Dex Mod or 11
Crystal, glass, ice The higher value of 11 + Wielder's Dex Mod or 13
Wood, bone The higher value of 12 + Wielder's Dex Mod or 15
Stone The higher value of 14 + Wielder's Dex Mod or 17
Iron, steel The higher value of 15 + Wielder's Dex Mod or 19
Mithral The higher value of 17 + Wielder's Dex Mod or 21
Adamantine The higher value of 18 + Wielder's Dex Mod or 23

Here are the adjusted Hit Point values. In general, we will assume weapons, armor, and shields are resilient objects. Objects must be adjusted by material and whether it is magical or not.

Base Object Sunder Threshold
Size Resilient
Tiny (dagger) 4
Small (longsword, shield) 6
Medium (armor) 8