From what I have gathered, each expansion will include two new mages with contrasting abilities or philosophies. Here’s my suggestion for such an expansion:

Spirit Weaver: “We are all part of the pattern. You are the threads and we, the weavers, will spin your story. For how can mere threads understand the part they are supposed to play in the greater design?”

Spirit Weavers from ancient legend and are rumored to be as old as the Gods. With the arrival of the Chaos Mages, they have come out into the open once more. While the Chaos Mage tears the pattern apart, the Spirit Weaver binds it together. The Spirit Weaver can turn your creatures to her purpose or summon transient creatures that attack immediately and then vanish. Her foe is never certain of the direction he will be attacked from next; it might even come from his own ranks!

Chaos Mage: “We come to you from a plane called Chaos. We come not to take your world from you, but to bring you into ours. Travel the void with us, free of the pattern, and forge your own destiny!”

The Chaos Mage is only partly in this plane. Dark and mysterious, his creatures can become portals into the unknown plane called Chaos, dragging weak or damaged monsters in that zone with them. When sacrificing his creatures in this all-or-nothing attack the Chaos Mage must exercise perfect timing, and any opponents must be on their toes to survive.