Endowment of Corrosion (Ignore this)

Due to various circumstances, you have become endowed with primordial energies of corrosion. Explain the origin of your newly awakened affinity; whether it is a divine blessing, the power of a bloodline, a strange coincidence, a deal with the (proverbial) devil, or some other fifth thing. What physiological changes has this elemental endowment brought about?

Your save DC for this subclass is 8 + your Constitution modifier + your proficiency bonus.

Elemental Physique

3rd level martial archetype feature.

You have resistance to acid damage and your unarmed and weapon attacks can count as acid damage in addition to their normal damage type. Additionally, you can eat pretty much anything. You are immune to any negative effects that would result from ingesting harmful substances and you can treat any organic material as rations.

Other creatures have advantage on Wisdom (Perception) checks made to detect you via smell. You also possess a secret and terrible weakness: soap. A bar of soap dissolved in a bucket of water would deal 1d4 poison damage to you. You are very clean, always. But you smell like acid.

Practical Proficiencies

3rd level martial archetype feature.

Your elemental endowment has effected you in an unexpected way! You are proficient with weaver's tools, cobbler's tools, leatherworker's tools, and tinker's tools. 

Corrosive Blood

3rd level martial archetype feature.

So long as you are not at full health, a creature that is in direct physical contact with you will take acid damage equal to your Constitution modifier at the end of every turn it remains in physical contact with you. Clothes or armor do not protect against this. Also you smell bad.

Although you have resistance to acid, your equipment does not. Whenever you roll a critical failure on an attack roll or saving throw, or whenever an enemy hits you with a critical success, one piece of narratively relevant equipment is damaged. If an item provides an armor bonus, then it's AC is reduced by 1 each time it is damaged, to a minimum of 0 (a common breastplate is destroyed after four hits, a +1 shield is unusable after three hits, etc.). A common item is unusable after being hit once, an uncommon item is unusable after being hit twice, etc. Items that provide acid resistance can't be corroded. Repairing an item requires the relevant proficiency or the mending cantrip. During a short rest, you can repair a number of items equal to your Intelligence modifier. You can repair all of your damaged items as part of a long rest. A repaired piece of magical equipment will usually recover its magic after a long rest.

Endowment of Corrosion Advancement Options

Choose one ability from the list. You can choose another ability from the list at 15th level.

Acid Bath

As an action, you can spray liquid acid within an area of 10 squared feet (two 5 foot squares). These squares can be arranged in any way, but they must be contiguous to one another and at least one of the squares must be contiguous with the square you occupy. On the turn you use this feature, a creature caught within the acid spray must make a Dexterity saving throw or take 4d4 acid damage on a failure and half as much on a success.

At the end of your turn, the acid soaked area becomes difficult terrain for 1 minute. Creatures who enter the acid take 4d4 acid damage for every 5 feet they move through it. Creatures who end their turn in acid take 4d4 acid damage.

You can use this ability a number of times per long rest equal to half your proficiency bonus rounded down.

The area of effect and the damage increase at certain levels. 10th level (15 sqft., 6d4), 15th level (20 sqft., 8d4), and 18th level (25 sqft., 10d4).

Caustic Cloud

Once per long rest, you can emit a cloud of corrosive gas that melts the skin and lungs of creatures caught within its area. The cloud has a faint yellow or green tint and it does not notably obscure vision. It lasts for 1 minute and occupies a 5 foot radius sphere, centered on yourself. The sphere spreads around corners and a wind of moderate or greater speed (at least 10 miles per hour) pushes the sphere at a speed of 5 feet per additional 5 mph over 10 mph.

A creature within the sphere must make a Dexterity saving throw when it first enters the cloud's area. If a creature ends its turn in the cloud, it must instead succeed on a Constitution saving throw. On a success, a creature takes 4d4 acid damage. On a failure, a creature takes 4d4 acid damage and accidentally inhales the gas, becoming poisoned. At the beginning of each of its turns until it succeeds, a poisoned creature must succeed on a Constitution saving throw or take 1d4 acid damage and remain poisoned.

A creature automatically succeeds this saving throw if it does not need to breathe or if it has resistance or immunity to acid damage. You are immune to this cloud only until the end of the turn it was created on. A creature immune to the poisoned condition can still be poisoned by this cloud, unless it does not need to breathe.

The radius and damage increase at higher levels. At 10th level (10 ft., 6d4 cloud damage), 15th level (15 ft., 8d4 cloud damage), and 18th level (20 ft., 10d4 cloud damage).

Corrosive Strike

If your attack roll results in a 19-20 on the die, you can choose one visible item that the target creature is wearing or carrying to become damaged. If an item provides an armor bonus, then its AC is reduced by 1 each time it is damaged, to a minimum of 0 (a common breastplate is destroyed after four hits, a +1 shield is destroyed after three hits, etc.). A common item is unusable after being hit once, an uncommon item is unusable after being hit twice, etc. If a creature carries no items and does not have resistance to acid damage, then its AC is lowered by 1. A creature's AC cannot be reduced below 10. Items that provide acid resistance are not effected by this feature.

At 18th level, the hit range for this ability becomes 18-20.

Soak

Once per turn as part of a weapon attack, you can soak a creature with acid. Until the start of your next turn, any time that creature takes damage, it takes an additional 1d4 acid damage.

You can use this ability a number of times per long rest equal to your proficiency bonus. This damage increases at 10th level (2d4), 15th level (3d4), and 18th level (4d4).

Targeted Solvent

As part of a long rest, you can experiment with a piece of organic or inorganic material, such as a piece of a corpse or a mineral sample, in order to adjust the properties of your acid. When you do so, any time you inflict acid damage against a creature or object composed of the specified material, the damage is increased by an amount equal to your Intelligence modifier. You can only target your acid against one type of material at a time. When you do so, choose one of the following materials to target. 

• Flesh
• Bone
• Scales
• Stone
• Metal
• Wood
• Fungus

Elemental Surge

10th level martial archetype feature.

You can enhance your action surge. During your action surge, all of your unarmed and weapon attacks burst into a shower of acid, creating a ten foot cone of acid that uses the attack and damage roll of the initial attack. The cone is aimed in the direction you're attacking and the point of origin is the creature you are attacking.

Elemental Progression

15th level martial archetype feature.

You gain immunity to acid damage and damage caused by your acid ignores resistances to acid damage.

Choose one option from the Endowment of Corrosion Advancement Options.

Corrosion

18th level martial archetype feature.

As a creature accumulates damage from your acid, the corrosion of its body begins to show its effects. A creature that takes acid damage from your attacks or abilities cannot regain hit points and subtracts 1d4 from all of their attack rolls and saving throws until the start of your next turn.