Los suenos son "de mentira"
It this says, Dreams aren't real, can't hurt you. Why not say "son mentiras"?
2 Answers
"Mentiras" would be "lies", implying a deliberate deception, but "de mentira" means fake, not the real stuff. For example, "una pistola de mentira" would be a "toy pistol".
By the way, when you connect words with "de" there is no agreement between them, especially because the second word is often a noun.
Una pregunta - ahora que lo se lo que significa "de mentira" ...¿Es possible de verdad que sueños puedan ser de mentira?