Westley being revived by the two men he rendered unconscious (situational irony)
In the first half of the film, Inigo and Fezzik were obstacles to Westley that he needed to knock out in order to save Buttercup. In the latter half of the story, however, the tables have turned as Westley is the unconscious one whom Fezzik and Inigo seek help from in order to kill Count Rugen. Not only is the person who is unconscious switched in these instances, but it's also ironic that the three began the film as enemies and end up partners in crime by its end.
The ROUS's (dramatic irony)
When Buttercup is sucked into the lightning sand and Westley dives in to save her, the viewer watches as an ROUS passes by while they're submerged. We are privy to the third and final danger of the Fire Swamp before our heroes are, which is an example of dramatic irony.
The grandson wants to hear about the kiss at the end (situational irony)
The bedridden boy begins the story completely averse to the romantic elements of the book; at any mention of kissing or sappy love, he interrupts or rolls his eyes. In an unexpected turn, however, he ends the film by asking to hear specifically about the kissing after his grandfather omits it, something that we didn't necessarily see coming, demonstrating his increased emotional investment in the tale.
Inigo inflicts the same 5 wounds to Rugen that he received from him (situational irony)
When Inigo kills Count Rugen, he does so by inflicting him with the same 5 wounds that Rugen gave to him: a slice on each cheek, a jab in each shoulder, and finally, a severe blow to the stomach. This is a classic case of role reversal as the attacker becomes the attacked, and in Inigo's case, the mirrored wounds serve to highlight that his killing Rugen is purely payback for the pain he's caused him.
