Evil Alex is the version of the original Alex Russo that she created of herself only meaning to make herself nicer in The Wizards Return: Alex vs. Alex.
In the end original Alex undid every spell she had ever cast Evil Alex. Evil Alex wanted to help Dominic destroy all the mortals, to get them in one small ball. Then Good Alex know Dominic was really the bad person. Evil Alex has very different look than Normal Alex (Good Alex.) Evil Alex had brown- white hair, red nails, a multicolored dress (Black, white, red) and the same boots as Normal Alex, brown normal boots. She and Dominic were dating and wanted to destroy everyone who's not a wizard, witch, vampire or any other creature with Dominic's machine, the Dominic 1000.
Mason Greyback had mistaken her for the Normal Alex.