Cymbeline's Ignorance
At the beginning of the play, virtually every character is aware of the Queen's malicious scheming and evil nature – every character, that is, except for Cymbeline himself. It is not until the end of the play (and the Queen's death) that Cymbeline comes to understand how the Queen led him and his kingdom astray.
Fidele
The plot surrounding Fidele is rife with dramatic irony, as the audience is aware that the boy is actually Imogen in disguise. When Fidele meets Belarius and the two (kidnapped) brothers, they feel connected to one another though they cannot explain why. The audience, of course, knows how everyone actually is. When Fidele is spared by Cymbeline, again, the audience understands the compulsion other characters feel to "protect" him, even when other characters cannot yet make sense of it.
Iachimo's Caution
Throughout the first half of the play, Iachimo cautions against trusting people, especially women. He condemns the notion of lying, dissembling, or pretending in order to better convince Posthumus that he is telling the truth about Imogen. The irony, of course, is that Iachimo is one of the central antagonists in the play (along with the Queen), and that he himself is deceitful and self-interested.
Britain's Tribute
At the end of the play, Cymbeline agrees to continue to pay tribute to Rome. This decision is ironic because Britain wins the war, but it ultimately helps conclude the play on a note of peace and harmony, something Cymbeline desperately wants after seeing how the Queen's influence disrupted his court and his kingdom.
