Double

Double is a Quirk possessed by Jin Bubaigawara.

Description
Double allows Jin to create a copy of anything, two at a time, through touch.

With Double, Jin can produce replicas of anyone to provide support in numbers. His clones possess the same personality and abilities as the original, making it hard to distinguish them from the real person at a first glance.

Jin has a limit of creating only two clones at a time, however, because he is able to copy himself and his copies also have access to Double, Jin is theoretically capable of producing infinite replicas of himself, as long as each clone gets to clone themselves and so on.

In order to conceive a perfect clone, Jin requires a flawless image of whatever he plans to duplicate. This includes having knowledge of precise measurements and features. The copies are less durable than the original thing, dissolving into a viscous liquid after suffering enough damage, and a second copy is apparently even more fragile. Worth mentioning is that Jin appears to be capable of detecting when clones get destroyed if he's not close to them.

Usage
Double had a major role in shaping Jin's character, to the point of making him insane. In the past, Jin would abuse Double to generate copies of himself to act as his servants and follow his bidding. However, due to Jin's clones sharing the same personality as the original Jin (who was lazy and overbearing), they disliked the slave work they were put in and ended up rebelling against their creator, wrapping him with ropes. As each clone felt they were the real Jin and the other fakes, they started fighting amongst themselves while the original Jin could only watch in horror as his own image kept attacking and killing itself repeatedly.

Having suffered a traumatic experience with this particular event involving his Quirk, Jin currently refuses to use his ability on himself. If he is left through long periods of time without covering his face with a mask, Jin, as he claims, will end up splitting himself. It's unknown if he is referring to an actual physical consequence or just a metaphor for his multiple identity disorder.

Having no qualms in replicating others, however, Jin is a very useful asset, as his Quirk grants him a way to temporarily increase the numbers of the League of Villains if they find themselves short-handed, giving the organization more "subordinates" to attack or distract enemies. As such, Tomura considers Jin a vital part of his villainous goals.

Trivia

 * This Quirk is functionally similar to Clones, as they both revolve around creating duplicates out of a viscous liquid. There are a few key differences, though:
 * Ectoplasm can only make replicas of himself, whereas Jin is capable of making doubles of anyone, including himself as well.
 * Ectoplasm can create up to 30 (36 at best) clones, whereas Jin is limited to only 2 clones of other people. It is worth noting that Jin can create as many clones of himself as he wants, as those clones can use their own Double Quirk on themselves to continuously multiply while bypassing the 2 clone limit.
 * Ectoplasm's clones can't use his Quirk, whereas Jin's clones can.
 * Ectoplasm can create a massive clone of himself, whereas Jin has not shown such an ability.