Gatewood Embezzling Money (Dramatic Irony)
Early on in the film, we see Gatewood, the banker, embezzling money from the bank that he works for and splitting town. Later, he is picked up by the stagecoach, whose passengers are a bit confused about why he is outside of town, but accept his assertion that he is simply leaving town. While the viewer knows that Gatewood is on the run from being found out, the characters do not know until the end. Throughout the trip, Gatewood is exceedingly combative, which we know is due to his anxiety about being found out by the authorities. The tension between our knowledge of Gatewood's crime and the other characters' naïveté creates an instance of dramatic irony.
Ringo Following Dallas Outside (Dramatic Irony)
This is a smaller instance of dramatic irony, but an iconic image in the film. At Apache Wells, Dallas walks down a long hallway to the moonlit outdoors. She doesn't see that Ringo is watching her as she walks down the hallway, but we watch him watch her. Thus, dramatic irony is created in the fact that we know that Ringo feels affection for and attraction to Dallas, while she doesn't yet know this.
Luke Plummer's Death (Situational Irony)
The viewer does not see the shootout between Ringo and the Plummer brothers, so immediately following, we do not know who has emerged victorious. As the saloon patrons wait to hear about the results, Luke Plummer opens the door of the saloon. For a moment, the viewer is meant to feel crestfallen, thinking that Luke has won and killed Ringo, our protagonist. After taking a few steps, however, Luke falls forward onto the ground, dead. Director John Ford plays with the viewers' expectations. For just a moment, we think that Luke is still alive and has won, but our perceptions are subverted when he turns out actually to be dead.
Curley lets Ringo go (Situational Irony)
At the very end of the film, Curley and Doc Boone pull up in a carriage to bring Ringo back to jail to serve a year for breaking out. Curley then sympathetically invites Dallas to take a short ride with Ringo to say goodbye. When Dallas gets in the carriage, Curley sends the carriage on its way, turning a blind eye to the outlaw's escape. This moment is surprising because it is not the outcome that we expect the Marshal to take. As the hand of the law, we expect him to take Ringo in and make Dallas wait for him, but instead, he is the one making it possible for them to escape together.
