Reality alteration was the result of a spell or ritual in which the very nature of a dimension was altered totally or partially, affecting timespace as well as the memories and perceptions of a dimension's inhabitants. Only beings with a hightened sense of self-awareness, like Adam, or beings "outside reality", like the mentally-ill, were capable of perceiving such changes.
- In Sunnydale 1997, Billy Palmer manifested as an astral body after he was beaten into a coma. Along with his consciousness, the nightmares of the people of Sunnydale manifested and modified reality. Willow accompanied a tenor on stage as a soprano to perform Madame Butterfly, Xander finds out he is in his underwear at school and is purchased by a evil clown, Giles forgotten how to read, Cordelia finds herself dressed and combed in a old-fashioned way and obligee to participate in the chess club, Buffy is rejected by his father, finds himself buried living being by The Master,released temporaly and becomes a Slaypire.
- In 1998, Anyanka granted a wish to Cordelia Chase, creating an alternate timeline in which Buffy Summers never moved to Sunnydale, causing the town to be taken over by the Order of Aurelius
- In 1999, Willow cast a spell to have her will done in an attempt to get over the pain of Oz's departure, but the exact wording she used caused anything she said to come true, modify reality, though only when she did so inadvertently. With this ability, she rendered Giles completely blind, made Xander a literal demon magnet, and caused Buffy and Spike to become engaged.
- In 2000, Jonathan Levinson performed an Augmentation Spell in order to make himself more popular. As a result, he became the best of everything, the ideal man. He became a seductor, author, actor, inventor, musician, military consultant and demon hunter. The spell, however, created an opposing force of evil, everyone's nightmare. Buffy caught on to the spell when she realized that Jonathan couldn't possibly have done everything he was reputed to have done if he had never left Sunnydale.
- Months later, monks of the Order of Dagon performed a reality alteration to give human form to The Key, effectively creating Dawn Summers. They also altered reality, as well as the memories of the Slayer, her family and friends, as well as all others who have ever been associated with Buffy Summers, to make Dawn fit into this new reality as if she had been naturally born.
- In 2001, Skip altered reality so that Cordelia Chase had become a famous and successful actress instead of a member of Angel Investigations. In this reality, Wesley Wyndam-Pryce had lost an arm due to a Kungai demon incident, and Allen Francis Doyle had passed his visions on to Angel, who, because of the stress of the power and the absence of Cordelia's humanizing influence, was driven insane.
- In 2002, Jasmine performed a spell to remove every record regarding the Beast, as well as wipe any memories of him, from this reality. The only person unaffected was Angelus, who, having been cursed, no longer technically existed.
- In 2003, the demon Cyvus Vail, acting on behalf of Wolfram & Hart, led a team of sorcerers and wizards in order give Connor, son of Angel, a new, normal life with a human family, and removing every memory related to him from the memories of the Angel Investigations staff. Only Angel, Cordelia Chase, Eve Levin, the Senior Partners and Vail kept memories of the unaltered reality.