Previous History in Kingdom Hearts
In Kingdom Hearts Birth by Sleep, Lady Tremaine's role is exactly identical to that of her film role. Treating Cinderella as a house servant and showing no love towards her, the wicked stepmother does all in her power to see that her daughters are successful in life. She is upset by their constant sibling rivalry, also showing an extreme affection for her devious cat named Lucifer, despite the animal's cruelty to Cinderella's mouse friends.
After discovering the identity of the maiden that had won Prince Charming's heart at the royal ball to be none other than Cinderella, Lady Tremaine immediately locked her in her room when it came time for Anastasia and Drizella to try on a single glass slipper that had been left behind when the girl fled. However, Aqua, with the help of Fairy Godmother, helped Jaq free Cinderella from her room and try on the slipper.
The Grand Duke took Cinderella to go back to the palace, leaving Lady Tremaine and her daughters extremely bitter. Enraged, Lady Tremaine used the jealousy in her heart to turn Cinderella's pumpkin carriage into an Unversed, the Cursed Coach, in an attempt to murder Cinderella and Aqua, but her scheme backfired when one of the fire bombs it produced landed on her and her daughters, blasting them away.
Role in Reconnect
In Reconnect, Lady Tremaine is revealed to have survived her attack from the Cursed Carriage by escaping the bombs flung from the Unversed creature and going into hiding to plan her revenge in secret. However, her plans were cut short when Maleficent kidnapped Cinderella and used the Heartless to plunge Castle of Dreams into the Realm of Darkness. Lady Tremaine and her daughters managed to survive thanks to Ansem Seeker of Darkness granting them the capability to survive the Realm's corrosive effects on the heart. Tremaine spent the next 10 years or so plotting a way to escape the Realm before it destroyed her, finally escaping that realm when Sora closed the DTD and thereby restoring all the worlds back to normal. Lady Tremaine and her daughters returned back to the Castle of Dreams unharmed, and therefore set out to restore their family name in the world.
During the events of KH 3D, Young Xehanort approached Lady Tremaine with an offer to join the Syndicate in exchange for control over her world in due time. The evil stepmother agreed half-heartedly, not willing to trust any incarnation of Xehanort after her last attempt in trying to control one of their servants failed miserably. Still, she was given a seat in the throne room of the Castle That Never Was.
Later on, she acquires the Fairy Godmother's magic wand after Anastasia finds it. Lady Tremaine, intent on ruining Cinderella's happy ending and stealing it for her own daughters (turning Cinderella back into her slave), uses the wand to reverse time to undo Cinderella's "happily ever after". She also enchants the glass slipper to fit Anastasia so that Cinderella never gets to try on the slipper herself, then uses the wand to enchant Prince Charming into forgetting Cinderella and marrying Anastasia instead. Most notably, she uses the magic wand to transform Anastasia into the mirror image of Cinderella (making her beautiful), and teleports the genuine Cinderella into a pumpkin, which becomes another Cursed Coach, and transforms Lucifer into its coachman, to take her far away from the palace and to her death.
Ultimately, Anastasia is her mother's undoing; she comes to feel reluctant to marry somebody under false pretenses- while she cares for the prince, he does not love her legitimately, and she cannot bear to live the rest of her life pretending to be something she is not, even if she has a beautiful face.
Furious, Lady Tremaine tries to turn both Cinderella and Anastasia into toads, but the Prince defends the two from the spell and reflects it back with his sword, turning Lady Tremaine and Drizella into toads instead. Anastasia then restores herself to normal before giving the magic wand to Cinderella so that she can undo all the wrongs that have been committed. During the end credits, Lady Tremaine and Drizella have been restored, but are wearing scullery clothes identical to those Cinderella used to wear, implying that they will be working in the palace under Cinderella's authority as their punishment for the cruelty she endured under her stepmother.
In Reconnect, Lady Tremaine is finally a boss to fight against. She wields a long, sharp sword that used to be the Fairy Godmother's wand before Lady Tremaine transformed into a weapon. During the battle, she will bombard you and your party with dark magic or with ice and blue beams mixed in with her green magic dust. These ice beams are very dangerous as they can freeze you solid and leave you open to her sword slashes or green spell beams. Be careful when attacking her because her sword can deal major damage to you, so avoid it at all costs while removing her of her 5 HP bars. When half of her HP is gone, Lady Tremaine will start to glow blue and green, immediately followed by her summoing a swirling green portal from the ceiling that can randomly fire a spell laser at you and your party, turning you into an animal for a few seconds.