This piece of literature demonstrates irony in such a way that would have been unheard of, before the Civil War. Twain introduces Dawson's Landing in Pudd'nhead Wilson after David Wilson has made a metaphorical joke about killing half a dog. The significance of this metaphor was to expose the mindset of the citizens at the time; they would be more scandalized about a man killing half a dog than owning and mistreating slaves. Word of the joke spread quickly and David Wilson later became "Pudd'nhead" for being a fool in the eyes of the townspeople. The irony of this is, he is elected mayor at the end of the novel after being vindicated by his defense in court of the Italian count accused of wrongdoing.
Another irony Twain employs in this novel is the concept of the nineteenth-century code of honor. Judge Driscoll and Luigi duel. Judge Driscoll admires and tells Luigi beforehand what an honor it is to duel an Italian. After the duel takes place, having discovered Luigi had killed a man before in his life, Judge Driscoll's attitude suddenly shifts and he tries to denigrate Luigi's reputation.
The most important irony demonstrated in the book is how nature and nurture are related. After Roxy switched baby Chambers with baby Tom, it didn't matter if the new Tom had 1/32 drop of black blood; he was raised FFV (by one of the First Families of Virginia) who were respected by all - yet he still grew up corrupt and distasteful enough for his own mother to expose him to everybody.