The Butterfly 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 Butterfly Miraculous holder, If the person has negative emotions the Butterfly Miraculous holder will psychologically manipulate them convincing the akumatized person that they are trying to help them by giving them the power to accomplish his or her goals once that person accepts the offer they transform into a new, superpowered form with a new personality regarding their circumstances, and they usually follow the desires of the Butterfly Miraculous holder. To speak with them, the Butterfly Miraculous holder can telepathically talk with them, and whenever they do, a butterfly-shaped light mask appears over both of their faces. Akumatization does not give its holder the power to use mind control on their victims. However, if necessary and for the sake of having leverage, the Butterfly Miraculous holder can also briefly cause their bodies pain to threaten them for disobeying orders, or remove their powers if the person is using their powers incorrectly. The akumatized beings are meant to be superheroes, but the Butterfly 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 victim 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. The Butterfly Miraculous holder can remove one's powers, releasing and purifying it. This action enables for another akuma to be made.
Akumatization is a very helpful superpower, but the Butterfly 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 Butterfly Miraculous holder to lose power when it comes to using Akumatization has yet to be revealed.
In "Mayura" however, this is shown to be actually untrue, as it is stated by Hawk Moth that Miraculous Holders can actually remain transformed even after using their power for an indefinite amount of time, as long as they have enough experience to do so.
It is unknown if Akumatization works on more than just humans, robots, animals, and kwamis, but Season 2 will have the answer.
"Robostus" reveals that akumas can affect machines like Max's robot as long as they have emotions.
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 Butterfly 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.
In "Zombizou," Caline Bustier almost manages to resist her akumatization.
Initially, the ability to cause pain to the akumatized victim and remove their powers was a fail-safe to prevent the akumatized person from using their power for evil.
In "Despair Bear", 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, different akuma, unlike what happens to Ivan when he is re-akumatized with the same akuma in "Stoneheart" or Alix in "Timebreaker", when she is re-akumatized with the same akuma due to it being from different points in time.
"Glaciator" reveals that the original body of the akumatized person can, in some cases, still physically remain.
As seen in "Sapotis", more than one person can be akumatized at the same time if they are both holding the same object the akuma affects.
In "Zombizou," it is shown that the person doesn't need to touch the akumatized object to be akumatized, or at the very least not to talk with Hawk Moth.
When people are akumatized, Hawk Moth can telepathically communicate with one villain at a time. And yet, shown in "Sapotis", that he can communicate with multiple villains.
Like Cataclysm, Akumatization does not need the Butterfly Miraculous tool to activate it.
Akuma means "Demon" in Japanese. Presumably, if the Butterfly Miraculous were being used to create heroes, not villains, it would be a different color butterfly that was created, and called something else.
In French, Hawk Moth (Papallion=Butterfly) tells his akuma to "darken the heart" of his victims.