Ellone, Final Fantasy VIII
Appearing as Squall Leonheart lies in the infirmary, Ellone is introduced to gamers as a mysterious woman with unknown powers to manipulate time. She appears to send the SeeDs back in time to act out memories from the past, including various battles with Laguna, for no apparent reason. She remains an enigma until later on in the game when the childhood memories of the SeeDs are restored and it’s revealed she was essentially Squall’s adoptive older sister who has been in hiding as many want to harvest Ellone’s power to time travel themselves.