Character Description and History
Isis is a good witch. Unlike many of the other characters in Mage, she is not an avatar--that is, she has just learned her magic by studying it, as opposed to, say, Kevin Matchstick, who gained his powers by being a reincarnation of King Arthur. She is very focused on charts, schedules, and systems, like the astrological system. She has a familiar, a cat named Blackball. Isis is very friendly and helpful, and simultaneously a bit scatterbrained and very efficient. Her sisters are also witches.
She aided Kevin Matchstick in the past, so when he found himself in need of some magical advice, he and his friends went to visit her and her husband, Bartholomew Gretch. She gives them a doobie-like drug that gives them all a vision of an evil creature that looms over everything, but they are interrupted in mid-trance when the Sprigginflints attack. Gretch goes out to fight them but is overwhelmed, and the heroes join the fray. Between Kevin, Kirby Hero, and Joe Phat, they get the Sprigs to run off. Gretch is very sick from the Sprigs' poison bite, but Kevin is able to heal him with the Bat. Anxious about Gretch's safety, she lends the heroes a van and sends them off.
After the heroes settle themselves in Montreal, she pays them a visit along with her sisters. (She has previously told Kevin that he is predestined to fall in love with her sister Magda.) They coven together and try to find out what's going on with the forces of darkness. They are able to sense the Pale Incanter's general pattern, and want to begin casting out the evil spirits. She and Wally Ut get in an argument: he doesn't think too much of her magic, and she has a similar opinion of him and his power (he has not yet demonstrated any actual effective magic at this point).
She talks to Gretch by enchanting their television so that it acts a Skype-like device, and checks on things at home. He's fine. Then she and her sisters leave to check on things with the other avatars in Montreal. We don't see her after this, although Magda continues to play a part in the action. Assumedly Isis is trying to help the heroes from behind the scenes.
Powers and Abilities
Isis can cast a wide range of spells, but they typically require a lot of preparation and magical supplies. For instance, she thought she could create an antidote to the Sprigginflints' poison, but it would take her days.
Spells she has cast in the past include a spell that makes the inside of her house bigger than it looks on the outside, a shrinking potion, a drug that gives you visions of the future, a hasten spell, a cloaking spell, a homing hex that sends her van back to her, warding spells, a healing ointment for Kevin's hand, and a kind of clairvoyance spell that allowed her and her sisters to sense the pattern of evil in the area. She also said she could consecrate areas to banish the "nasties" that live there.
The power of Isis and her sisters is probably less than that of Wally Ut, as Magda was unable to remove a warding spell that Wally made.