After defeating any villain, like an akumatized villain, Ladybug throws the object she got using Lucky Charm into the air, yelling "Miraculous Ladybug!" This generates an explosion of pink energy, eventually dispersing into small ladybugs that fly around Paris and fix any damage done since the appearance of the villain, including reverting death.
As indicated in the third issue of Miraculous Adventures, the Miraculous Ladybug might be able clean up any damage, not just damage caused by a villain. Victory and other superheroes expect the Miraculous Ladybug can clean up their catastrophic damage in order to destroy the Trash Krakken, but Ladybug worries if it will be able to restore that much damage.
While using Lucky Charm causes Ladybug to start losing power, using Miraculous Ladybug does not, it being an optional power she can use before she detransforms.
In the Korean version, the Miraculous Ladybug is called "Miraculous Healing Light."
The Miraculous Ladybug not only fixes the villain's damage but can also fix the damage done by Cat Noir's Cataclysm and other general problems; for example, it fixes Alix's broken watch and rejoins the double Ladybugs and Timebreakers caused by time travel in "Timebreaker".
When the Miraculous Ladybug comes out of the Lucky Charm object, it makes the shape of the Wheel of Life.
The power of the Miraculous Ladybug is only limited to the apparition of the akumatized villain and can even revert death within that time.
To summon the Miraculous Ladybug, Ladybug always throws in the air the object summoned by Lucky Charm, even when it is impossible for her to retrieve it:
The coin used in the vending machine in "Mr. Pigeon".
The windup toy in Darkblade's armor in the episode of the same name.
The car jack in Animan's mouth in the episode of the same name.
The episode "Ladybug & Cat Noir (Origins - Part 1)" is the only one so far in which Ladybug doesn't use this superpower.
Despite using Lucky Charm, which creates a record player, Ladybug doesn't utilize the Miraculous Ladybug before she detransforms in "The Bubbler". She also doesn't utilize it with the pen in "Dark Owl" and the teapot in "Sapotis"
In "Simon Says", Ladybug uses it after Hawk Moth's final scene and before she captures and frees the akuma because she needs to fix her broken yo-yo.
She also uses it before capturing the akuma in "Pixelator", because she needs her arm to be healed before she can use her yo-yo.
In "The Collector", she uses it to bring her yo-yo back from the Collector's book in order to capture the akuma with it.
In some cases the Miraculous Ladybug (superpower) can't fix or restore an object that doesn't have any remains left to fix.
Following Santa Claus' hat in "A Christmas Special," Ella's and Etta's hats in "Sapotis" and Marinette's bracelet in "Gorizilla."
↑November 2015 per Thomas Astruc in https://twitter.com/thomas_astruc/status/666886344602423296
Kartos "@Thomas_Astruc can Ladybug revert or heal injuries and death inflicted by akumas with her "fixing" power?"
Astruc "@Kartos Anything"
Kartos "@Thomas_Astruc :O I'm assuming the amount of time she can go back to "undo" is very limited?"
Astruc "@Kartos limited to the apparition of the akumatized villain."