A unique variant or UV on a weapon or armor piece is a special enhancement on the item, that is not present on all items of its type. For example, a Nova Driver with Attack Speed Increase: Medium fires slightly faster than Nova Drivers without such a UV. A UV is a kind of ability; the Abilities article describes the kinds of UVs, how much effect they have, and how they combine with other kinds of bonuses. An item may possess up to three UVs.
There are two ways to acquire unique variants. First, when crafting (or upgrading) an item, there is a low probability that the item will acquire one or more UVs. Second, the vendor Punch in the Bazaar lets you apply UVs to any weapon or armor piece. In both cases, you cannot choose the UVs that you obtain; they are randomized.
There is a low chance of creating a unique variant each time that you craft a new item. The chance to get a UV on bombs seems to be around 10%  Better UVs are less likely to occur. Here is a breakdown of how often each degree of UV has been observed on bombs: 
- Low: 65.74% ± 8.95%
- Medium: 21.30% ± 7.72%
- High: 7.41% ± 4.94%
- Very High: 5.56% ± 4.32%
Another study estimated the probabilities at 66.67%, 27.41%, 4.44%, and 1.48%.
When crafting or upgrading, unless an existing unique variant bonus is explicitly transferred to a new item (as described below), each step in the item creation process provides a new chance at a new unique variant. For example, a unique variant may appear when initially crafting a cutter, as well as when the cutter is upgraded into a striker. For items with long crafting chains, this may provide as many as four chances at obtaining a unique variant bonus per item.
When upgrading, it is possible to transfer an existing unique variant bonus on the base item to your upgraded item. In the upgrade menu, the option to transfer the unique variant bonus to your upgraded item is pre-selected. If you de-select this option when upgrading, the resultant item will not retain the existing unique variant bonus. It will, however, have a chance at becoming a new unique variant, with a new unique variant bonus or nothing.
Due to the ability to transfer a variant through multiple steps, a relatively economical way to obtain unique variants is to mass produce the first item in a crafting chain. For example, a unique Ash of Agni can be produced by crafting a large number of Fiery Vaporizers and upgrading only the bomb that has the desired unique variant.
Unique Variant Tickets
In the Haven bazaar, you can meet Punch, the variant smith. For a price, he will remove all UVs from the selected item (if any), and re-apply the desired amount of randomly chosen unique variants to it. The price of his services rises sharply when you decide to apply more than one simultaneous unique variant to an item:
- 1 unique variant = 20,000 crowns
- 2 simultaneous unique variants = 75,000 crowns
- 3 simultaneous unique variants = 225,000 crowns
An item will never obtain multiple identical unique variants; for example, a sword will not gain more than one charge time reduction bonus from unique variants. Unique Variants already on an item can be locked when using Punch's services, allowing you to customize and perfect your item.
Types of Unique Variants
In general, weapon bonuses will make your weapon more effective. Bonuses are not equally useful for every weapon. For example, charge time reduction on bombs such as the Haze Bomb and bombs in the Vaporizer Series is a lot more useful than a damage bonus since such bombs are used for inflicting status rather than dealing damage.
Weapons can gain any of the bonuses listed below. These bonuses seem to be percentage based depending on the base stats of the weapons, check the Abilities for such info.
- Attack speed increase (ASI) (can't be obtained on bombs)
- Charge time reduction (CTR)
- Damage bonus vs (construct, gremlin, fiend, beast, undead or slime)
Weapon UVs come in Low, Medium, High and Very High. Weapon UVs are never Ultra or Maximum.
A total bonus of Ultra or Maximum can be obtained by combining the UV with the inherent bonus on a weapon or armor as explained in the Abilities article. For example, a Combuster UV ASI Very High will become Maximum when a Vog Cub Coat is equipped since the Vog Cub Coat has Sword ASI Medium. The Character Tab displays the combined abilities of weapon bonuses.
Helmets, Armor Suits, and Shields
Armor unique variants focus on adding protection against damage or status effects. Unique variants can either add defense against attacks that the armor would not normally protect against or stack with existing defenses on the armor.
Possible types of unique variants are:
- Bonus protection from normal, piercing, elemental or shadow damage
- Bonus resistance against stun, freeze, poison, fire, shock or curse status
After the 3rd August, 2011 patch, it is no longer possible to acquire sleep resistance as a UV.
Bonus damage protection, much like base damage protection, increases with the star-rating. For example, a low elemental UV on a 4* helm could appear longer than a medium elemental UV on a 2* helm. This assumption is made based on watching the tooltip, and remains untested.
The possible UV values an armor can have are: Low, Medium, High, Maximum. There are no Armor UVs with the values of Very High or Ultra.