You didn't really see a ghost - it was only imaginary.
You make up imaginary enemies and are chased by them.
All the events described in this story are imaginary.
All the characters in this book are imaginary.
I don't believe that Santa Claus is imaginary.
You say Nessie is an imaginary being, but I think he exists.
All her imaginary happiness vanished in a moment.
The dragon is an imaginary creature.