The greatest irony in Dr. Faustus is his hubris(excessive pride), and his faith in his own mortal powers to command the service of devils. in the end, he is torn limb from limb, and his soul is cast into the doom of Hell through his unwise decisions.
Structural Irony is present throughout Faustus as a whole. Marlowe presents this structural irony through the traditional use of an unreliable or naive narrator: Dr. Faustus is smart, ambitious and proud of his accomplishments, but refuses to recognize the faulty reasoning which eventually leads to the loss of his soul. Upon graduation, he rejects professions in law, medicine, theology and philosophy, believing that he is destined for something infinitely more satisfying, such as an omnipotent destiny filled with power and worship by the masses. This structural irony is supported by different types of irony such as dramatic and situational irony throughout the play.
An example of situational irony occurs when Faustus summons Mephistopheles, a demon who is servant to Lucifer. In exchange for twenty four years of power, honor and earthly riches, Faustus aims to sell his soul to Lucifer. The Good Angel attempts to dissuade him from such a disastrous course of action, but the Bad Angel tells him that all his fears are just inconsequential nuisances in his quest for self-fulfillment. Faustus falsely believes that he will never be called to account for his deadly decision as he believes that hell is a myth; however, we readers know that the Good Angel is actually right.
When Faustus asks for a wife after he seals the deal with his own blood, the devils tell him that the option of holy matrimony is now beyond his reach. Instead, they send him a succession of prostitutes for his sexual enjoyment. In the meantime, Beelzebub, Lucifer and Mephistopheles entertain him with absurd and entertaining manifestations of the seven deadly sins. This is dramatic irony, where the reader knows something the character does not seem to be aware of: the reader knows that the devils want to lure Faustus into a false sense of security. Another example of dramatic irony is when Faustus continually questions Mephistopheles about the universe and the primary concept of life but is constantly rebuffed with the admonishment 'to think on hell.' We know this is another way to lull Faustus into deeper and deeper indiscretions.
Another example of situational irony comes in the final stages of the play when Faustus gives way to despair instead of repenting. He begs for more time from the devils and asks Mephistopheles to summon Helen of Troy for the scholars, thinking that this will buy him the time he needs. He would rather have a dalliance with fantastically conjured up images than repent of his sins. In the end, his fate is sealed: two scholars eventually find his horribly mutilated and dismembered body. He loses his soul to Lucifer.