Mohun's Hypocrisy (Dramatic Irony)
Mohun keeps on saying and implying to other people that he is a progressive person—for example, in his contempt for the Tulsis, who celebrate all major Hindu festivals and follow sacred rituals. He supports the Aryan philosophy and is dismissive of Hair's duties as a pundit. But, despite his progressive principals, he expects a dowry for marrying Shama. He lives in their house, works in their employment for several years, yet continues to accuse them of robbing him.
Mohun Hating Shama (Dramatic Irony)
Mohun mentions at several places that he hated Shama and her family. He constantly berates her, and he even writes stories in which the protagonist is burdened by four children and is in love with a young, untouched, barren woman. Yet, at the same time, he expects Shama to be at his beck and call. He is sexually active with her, but every pregnancy surprises him and feels like a conspiracy from her and her family to trap him.
The Subordinated Main Character (Dramatic Irony)
With the narrative of the story focused on Mr. Biswas and his name in the novel's very title, it's plausible for the reader to suppose that he will be the main focus and driving force of the narrative. It is sadly ironic, then, that Mr. Biswas seems to be used and defined by everyone around him—from the pundit who denounces his birth, to the Tulsis who subordinate him. As readers, we have the experience of reading a story that appears to have the uncomfortable quality of being "about" a secondary, or even, tertiary, character.
Self-Fulfilling Prophecies (Dramatic Irony)
Like Oedipus in Oedipus Rex, Mr. Biswas ends up inadvertently fulfilling prophecies about himself. When Biswas is born, the pundit foretells that he will "eat up his mother and father," and that he could end up becoming a liar. In trying to be responsible while tending a calf, Biswas ends up setting off a chain of events that leads to his father's death; in trying to live an authentic, self-determined life, Biswas ends up (arguably) deceiving himself, and everyone around him, about what he needs to be happy, bringing his sphere of influence further misery.
