This marks the first time the Dalek casings are opened, exposing the creatures within them.
This story was originally meant to be the final end of the Daleks.
This episode was wiped by the BBC and no copy of it is known to exist.
This is the only final episode of a season that is not currently known to exist in the BBC archives from the entire 26 years run. Whilst The Reign Of Terror from Season 1 and The Wheel in Space from Season 5 are also incomplete, their final episodes exist.
The mold for the top of the Emperor Dalek's head is based on a Chumblie from the Dr. Who story "Galaxy 4".