Amy is a witch. Although initially starting off as a seemingly good-natured individual, Amy gradually grows to misuse her magic, eventually ending up as an enemy to Willow and her friends, becoming a bona fide villain in the series' continuation.
Amy continues to attend Sunnydale High and reappears in several more episodes; along with Jonathan Levinson and Harmony Kendall she is one of many recurring student characters. In the Season Two episode "Bewitched, Bothered and Bewildered", Xander Harris discovers that Amy has inherited her mother's power, having become a potent, if sometimes ineffective witch. Xander decides to blackmail Amy into helping him perform a love spell on Cordelia Chase, however, the spell goes awry and causes the entire female population of Sunnydale, sans Cordelia, to become obsessed with Xander. Caught in her own spell, a jealous Amy invokes the goddess Hecate temporarily turns Buffy into a rat. She is eventually forced by Rupert Giles to undo both spells.
By Season Three, Amy has joined a coven with Willow (now a practicing witch) and warlock Michael Czajak. In the episode "Gingerbread", the parents of Sunnydale (under the influence of the demonic Hans and Greta) become insanely paranoid about the supernatural's influence on their children, and prepare to burn Amy, Buffy, and Willow at the stake. To escape her bonds, Amy turns herself into a rat, but then, being a rat, she is unable to remove her own spell. Willow captures Rat-Amy and keeps her in a cage until she can be restored. Willow makes several unsuccessful attempts to "de-rat" Amy over the next two seasons. In the Season Four episode "Something Blue", in what writer Doug Petrie describes as "as cruel and funny as anything could be", Willow, who at the time has the power to have anything she says happen, accidentally turns Amy back into a human; however, Willow does not even notice, and a few seconds later accidentally changes her back into a rat.
Amy's final appearance in the television series occurs in the Season Seven episode "The Killer in Me." When asked her feelings about Amy's actions in this episode, Elizabeth Anne Allen said, "I think after all the things that she went through, there were a lot of reasons why she was so angry.
Having transformed aesthetically into Warren Mears, whom she tortured and flayed in a rage over the murder of her girlfriend Tara Maclay, Willow seeks help from the UC Sunnydale Wicca Group and discovers that Amy is a member. Amy explains that she had hit "rock bottom", and was doing much better now. It is soon revealed that Amy is in fact responsible for Willow's transformation, the result of a hex placed on her apparently out of jealousy and spite. However, in the Season Eight comic book, it turns out that this seemingly random event is actually part of a larger plan orchestrated by Warren, after Amy rescued him from death in the earlier episode "Villains."
Allen says she would have liked to explore Amy's struggle to overcome her anger, so that she could "get a grip and come back to the fold with her friends.
In the first issue of the Season Eight comic book story "The Long Way Home," Amy is discovered by the United States Army during an expedition to be living sixty feet under the Hellmouth after its collapse with her "boyfriend," an unrevealed creature whom General Voll regards with disgust. Her first words to an exploratory member were, "I'm gonna help you kill her." In exchange for their cooperation, Amy requests unlimited access to all the government's magical hardware as well as a weapons lab for her "boyfriend"; and if they succeed in taking Buffy down, Amy wants full immunity and release for the both of them.
Amy attacks Buffy at the Slayer's base in Scotland, putting her under a mystical sleep which only a kiss of someones love can undo. Raising an army of kilted zombies to battle the Slayers, Amy battles Willow mid-air before being stepped-on by Buffy's now-giant sister Dawn Summers. As Willow magically probes Amy's whereabouts, she suddenly senses a trap and is pulled through a portal, only to be "greeted" by a saw-wielding and skinless Warren Mears. As Warren tortures Willow, Amy faces off against Satsu and an awakened Buffy, who manages to channel enough of Willow's magic to defeat a demon which Amy conjured. Having seen her dreamspace while asleep, Buffy takes the form of Amy's worst nightmare: her mother. Distracted, Amy fails to notice a grenade thrown at her feet by Satsu, and as Buffy and Satsu charge into the room containing Willow, they see Amy appear and teleport away with Warren in her arms.
Later, in "Time of Your Life", she and Warren are shown working under direct orders from Twilight, under whom Voll served. Together they have constructed a missile, covered in mystical runes and candles, and targeted it at the Scottish citadel where the Slayers reside.