Akumatization (unconfirmed name) is a special superpower granted by the Moth Miraculous to its holder. It is the power to give power to other people.
The Moth Miraculous holder infuses energy into a butterfly, transforming it into an akuma. They release the akuma to find and transform a person they have chosen. Once the akuma reaches the person, it possesses an object that is meaningful to them, and it creates a telepathic link between the person and the Moth Miraculous holder. The person transforms into a new, superpowered form, and they usually follow the desires of the Moth Miraculous holder. To speak with them, the Moth Miraculous holder can telepathically talk with them, and whenever they do, a butterfly-shaped light mask appears over both of their faces. If necessary, the Moth Miraculous holder can also briefly cause their bodies pain, like to threaten them for disobeying orders. The akumatized beings are meant to be superheroes, but the Moth Miraculous holder can also make them supervillains, Hawk Moth creating the latter for evil intentions.
For the akumatized person to revert back to normal, their akumatized object has to be destroyed, freeing the akuma. Additionally, if the akuma isn't purified, it will duplicate into multiple copies of itself and transform other people into frozen physical copies of the original host. Those in the frozen state do not move again until the original host is akumatized again, and they follow the original host's directions. One way to purify the akuma and turn it back into a regular butterfly is with the Ladybug Miraculous holder's yo-yo, but no information has been revealed about if the Moth Miraculous holder can purify the akuma themselves.
Akumatization is a very helpful superpower, but the Moth Miraculous holder can only make one akuma at a time, the only time there are multiple being when the akuma duplicates.
Using Miraculous superpowers results in the holder losing power and having to detransform about five minutes later. What causes the Moth Miraculous holder to lose power when it comes to using Akumatization has yet to be revealed.
It is unknown if Akumatization works on more than just humans and animals like kwamis, but Season 2 will have the answer.
Sometimes, animals or objects are indirectly transformed with the akumatized person, including Roger Raincomprix's car in "Rogercop", Jagged Stone's alligator, Fang, in "Guitar Villain", and Santa Claus' horses in "A Christmas Special".
Akumatized villains are chosen by Hawk Moth because of their negative emotions, like sadness or anger, but it's unknown if akumatized heroes have to feel the same type of emotions to be sensed and/or transformed by the Moth Miraculous holder.
Hawk Moth specifically goes after people who are in despair and are not happy because it is easier for him to manipulate people into doing bad things.
If the person isn't despaired enough, they can refuse the akuma.
Hawk Moth can take away the power of akumatized people and cause them pain. This gives him leverage.
Initially, this was a failsafe to prevent the akumatized person from using their power for evil.
People can be akumatized more than once, though it's unknown if their second Akumatization has the same or a different appearance.
By second Akumatization, it means a second akuma. This is unlike what happens to Ivan as he is reakumatized with the same akuma in "Stoneheart".