The big irony in this short story is how the hunter becomes the hunted. In his usual life, Rainsford is a big game hunter extraordinaire. When he is placed in the "game" with General Zaroff, he becomes the prey rather than the predator. In addition, Rainsford first responded to Zaroff's invitation to the game with shock and disbelief. However, once he is forced into the "survival of the fittest" scenario, we are led by Connell to believe that Rainsford kills Zaroff and sleeps in his bed. The contrast here is that Rainsford, the very person who was so appalled by the idea of murder, has to kill Zaroff to end the plot.
In "The Most Dangerous Game" the irony--a contrast between what is expected and what actually happens--is the fact that Rainsford, who responds with umbrage to General Zaroff at dinner the first night that he does "not condone cold-blooded murder," becomes a cold-blooded murderer himself. For, after being filled with terrror and feeling like "an animal at bay," Rainsford escapes his predators and returns to become himself the predator, who after killing General Zaroff, feels as did Zaroff, no compunction: "He had never slept in a better bed, Rainsford decided."