Mandi

Mandi was the room mother for Wyatt's preschool class. Shortly after the Charmed Ones faked their deaths, a possessor demon took over Mandi in hopes of using Wyatt to bring back The Source. She intended to raise Wyatt as her own son and turn him evil.

"Mandi" gained Wyatt's trust by showing that she was magical as well, and eventually got him to use his powers around her.

Piper got suspicious that Mandi was acting like the perfect supermom, but only thought that Mandi was trying to get under her skin. She didn't think anything else of it until "Mandi" took Wyatt to Magic School, which had been overrun by demons. She blew her cover, however, when she took Wyatt out of the preschool and didn't take her own son with her. "Mandi" then cast a spell to bring back the Source, and Wyatt sealed it by putting his finger in a chalice.

The Charmed Ones were able to use a spell to eject the possessor demon from Mandi, and vanquished both her and the Source shortly afterward.