VIDEOS:
"Topaz's" reflection
When Simon possesses Topaz, his true form is reflected in a mirror, which is how the BFFL realize his trick.
Example of:
The Mirror Shows Your True Self
Vampire Martin
Example of:
Classical Movie Vampire
The Little Mermaid
Example of:
The Mirror Shows Your True Self
Time's Arrow
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Rage Against the Reflection
Ghostbusters (1984)
Example of:
The Mirror Shows Your True Self
Elena of Avalor
Example of:
The Mirror Shows Your True Self
Equestria Girls
Example of:
The Mirror Shows Your True Self