Regina is Clara's mother. She created the Nutcracker land by bringing all the realms together
Zelena is Mother Ginger
The entire movie was one of Sergey Taboritsky's psychotic episodes.
- The Four Realms are a deranged, hallucinatory version of 18th/19th century Europe when the Romanovs whom he worships ruled Russia, and the events which occur therein revolve around prince(sse)s, regents and the concept of the Rightful King Returns, much like how he establishes himself as Regent for Life paving the way for Alexei's return. The big central palace even has Russian-inspired architecture and giant clockworks, the latter being a common theme of his obsessions.
The story takes place in the same universe as Toy Story.
It centers on a device that brings toys to life. Clara, per the novelization, tries to figure out a way to allow her friends from the Realms to visit her world. She succeeds, but an accident with the machine brings all toys to life. To avoid chaos, the toys agree to pretend to be inanimate when humans are around.