A nine-lifed enchanter is the most powerful types of enchanter on existence. The posessions of nine lives means that they have no counterparts within the nine worlds consisting the series. Thus if a nine-lifed enchanter is born in Series 12 A, he or she would have no counterparts in any of the other worlds in the series 12; i.e. 12B through 12L. This type of enchanter, thus, is extremely rare and only they can have the title Chrestomanci.
It has been suggested that the nine-lifed enchanter contains, concentrated in a single person, all the power that would have been spread out among the nine versions of that person. In The Pinhoe Egg, Chrestomaci says (about Eric 'Cat' Chant) that "... In Cat’s case, eight other people just like him either failed to get born in the other worlds of our series, or they died at birth. Most of them would probably have been enchanters, too. Cat has nine people’s magic...”
Certainly, the nine-lifed enchanter's power is somehow related to the cross-series duplication. Gabriel de Witt mentions in The Lives of Christopher Chant that if a nine-lifed enchanter consistently loses lives in an unusual way - for instance, by going astral travelling with a spare life and letting that life get killed instead of the one he was actually due to lose next - the resultant bending of the natural order causes problems not just in his own world but throughout his series.
There is some doubt about exactly what is meant by a nine-lifed enchanter not having any duplicates. In The Lives of Christopher Chant, Mordecai Roberts says that a nine-lifed person comes about when "all the doubles you might have had ... were never born for some reason", but this is not put to the proof, and in Charmed Life we hear of a nine-lifed enchanter who had at least one double, in the next world along, who died when he was born.
An enchanter's spare lives can, with magic, be removed intact and stored elsewhere, to prevent him using them - or accidentally losing them. In World 12A, the technique was pioneered by Gabriel de Witt while he was Chrestomanci, and took several hours of exhausting work for himself and three assistants (including a doctor to monitor the subject's physical health and an astral travel practicioner to keep an eye on the subject's spirit). In Series One, there is a Mage-built weapon that can do the same thing in moments.
Having nine lives does not appear to give one a greatly extended lifespan. If one dies of old age, the new life taking over will make improvements specific to the actual cause of death, but there will not be general rejuvenation: one will still be old, and will die of old age again before very long. In any case, nine-lifed enchanters tend to live in interesting times and use up most of their lives in other ways before getting a chance to die of old age.
Nine-lifed enchanters usually have a weaknesses. Christopher Chant, for instance, cannot work magic when in contact with silver, and Eric Chant can only work magic through his left hand. The reasons for the existence of such a weakness is unknown. It has been speculated that the reasons might be of a hereditary nature/trait.
They are typically a great deal stronger than even other enchanters, and can even disposess the latter of their powers completely; as demonstrated by Gabriel de Witt taking away the magic of another enchanter, Ralph Whetherby Argent. They can also overcome almost any other magic users with relative ease; for instance when Christopher Chant withstood the might of a virtual army of withches and warlocks by himself, and at another point debilitating the white devil herself with a simple gesture.
Whether or not all nine-lifed enchanters are equally powerful is also unconfirmed; however, Christopher suspects that Eric ('Cat') Chant might be a stronger enchanter than himself, once Eric sets his mind to it. Christopher is also shown to be rather weary of Eric at certain instances. It is, however, implied that Christopher and Eric have very different wavelengths when it comes to using their powers; their magic (while falling within the same paradigm of enchanters magic) are considerably different, with the latter bearing a greater affinity towards natural magic (i.e. 'of nature'). In The Pinhoe Egg, Cat says (about Chrestomanci) that "... Chrestomanci almost never could turn
anything back once Cat had changed it: their magic seemed to be entirely different ..."