Wilford's Heir (Situational Irony)
At the end, Wilford offers Curtis the opportunity to become the new conductor of the train and take his place as the figurehead. Curtis has fought so hard to get to the front of the train, staging a bloody rebellion and causing the train a great deal of trouble. Ironically enough, however, Wilford admires Curtis' formidable spirit and sees the revolt as helpful to the well-being of the train. While the viewer expects a contentious confrontation between Wilford and Curtis, Wilford is far gentler, and views Curtis as a protege of sorts.
Curtis crashes the train to save it (Situational Irony)
Instead of taking Wilford up on his offer to be the new conductor of the train, Curtis chooses to stay true to his beliefs and his contempt for the hierarchy that has so oppressed him on the train. In order to take down the empire that Wilford has built, he must crash the train and make it stop running, sacrificing many lives so that his ideals might survive. This scenario is ironic because, even though Curtis wants to save his people from the tail car, he ends up killing many people in the process with the faint hope that the destruction he causes will make way for a new start for some.
CW7 and the Ice Age (Situational Irony)
The film starts with an ironic premise. In an effort to counteract the destructive effects of climate change, human beings have released a chemical called CW7 into the atmosphere, but rather than help the situation, it has plummeted humanity into an Ice Age, an arguably worse environmental fate than the slow development of global warming.
Gilliam is in league with Wilford (Situational Irony)
Gilliam is Curtis' mentor. Curtis looks to him for advice about when to revolt, and deeply respects his opinion as an elder. At the end of the film, Curtis learns that Gilliam has been in league with Wilford the entire time and helped orchestrate the revolt with Wilford in order to control the population on the train. This ironic twist shows that everything Curtis has done, all of the deeds he thought were so heroic and helpful to his cause, were part of Wilford's plan.
