Every year, two times a year, the Heat occurs. Unmated females with their first heats are let out in an expanse of territory where they are forcefully mated and claimed by the unmated males.
This year is Cassandra's first heat. And she is deter...
You already know Cassie and Fenris, but what about the others?
Geri
Freki
Lycaon
Morrigan
Teras (the Beast)
And finally these, which are the soul-shapes of Amarok and Fenrir's wilds. This means that Up There, when Cassandra was created, the wolf that had chosen Amarok once, decided that Cassandra was worth her presence. That's how reincarnations of souls work in Wolrth. This also means that when the Wolfseer said Amarok had come back, she wasn't completely right. Amarok's wild came back. If Amarok had come back, Cassie's wolf form would be Amarok's personal wolf form, which is not the case.
Amarok's wild's soul-shape
Fenrir's wild's soul-shape
The art belongs to the creator. In most cases in this cast, the wolves belong to Kipine, on DeviantArt. I'm not sure about the rest of them.
A/N) And here's the rest of the cast! Hope the second part cleared up some things