Siba-Noor is a powerful Xalician shaman that appeared in the children's book The Legend of Yaotl. Whilst Siba-Noor was out on a sojourn, the warrior king Yaotl and his army were destroying her home. Siba-Noor sensed this and returned home, but it was too late; not only had Yaotl and his people destroyed Xalica, but he had also unleashed a band of unruly and destructive creatures. Understandably angry with this turn of events, Siba-Noor cast a spell which would turn Yaotl's generals into unmoving, undying stones and also force Yaotl to live forever with the pain of the repeated loss of loved ones.
Siba-Noor is also name-dropped in an exposition by Winters in the junior novelization of the film.