Irony of Appearances
Those who appear to have their lives most put together actually do not; Frank, for example, looks to be a successful, reliable businessman but is in fact a robber and murderer. Edie looks harsh but is actually understanding, and Floyd comes across as odd and eccentric but is really a good friend underneath the exterior.
Irony of Parental Control
Grandad allowed Chap to have lots of freedom, encouraging him to go outside and have fun adventuring, but that was only to make up for the fact that he himself could never do those things because of severe social anxiety.
Irony of Disguises
Cassiel, Chap, and Frank all wear costumes to disguise their faces on the nights of Hay on Fire, but ironically the times when they wear the disguises are the times they allow their characters to be more fully revealed; Cassiel talked to Floyd the night of the festival, Frank tried to kill both Cassiel and Chap, and Chap revealed himself to Frank and Edie while in costume.
Irony of Impersonation
Chap chose to impersonate Cassiel because he thought it would give him the easy life he desired, but it turns out that pretending to be someone else is exhausting and forces him to live with more anxiety than he had before.
Irony of a Stolen Family
When Chap assumes the role of Cassiel, he thinks the family he will be joining will be someone else's. However, by the end he realizes that he is in fact part of the family, being the long-lost twin of Cassiel, and so had been pretending to be a stranger to his own family for the entirety of the book.
