As Raven starts to tell Starfire about herself, she mentions "I was born in a place called Azarath." Azarath is part of her mystical spell, "Azarath, Metrion, Xinthos." Incidentally, Metrion and Zinthos are not references to anything and were created for the series. Raven's mother Arella, involved in a mystic cult, was chosen to become the bride of the demonic Trigon. Arella later discovered she was pregnant and she was taken in by the pacifistic disciples of Temple Azarath, a group who had centuries earlier forsaken life on Earth to pursue their own nonviolent lifestyle.
Originally, the creative team toyed with the idea of letting Hynden Walch do Raven's voice and Tara Strong do Starfire's voice when they switched bodies. They tried it out in the recording session. Hynden did a really good Raven, and Tara did a really good Starfire - both women are so talented that the creative team couldn't tell the difference. In the end, they just decided to go with the original plan.
The voice of the Puppet King is based on the voice of 'Peter Lorre'.
Both Starfire and Raven have very different personalities and backgrounds which affects their powers. On Tamaran, Starfire's home planet, everyone is very open with their emotions. By contrast, Raven keeps her emotions bottled up so her evil side is not released.
Even though no actual changes were made to the appearances of Starfire and Raven, the two look different when their bodies are switched. Raven suddenly appears weak and helpless, while Starfire seems older, more mature and looks more like Blackfire.