This is an example of verbal irony because Fortunato is not actually "Luckily met" like Montresor says. Montresor knows the truth and he is purposefully ironic in this scene.
Fortunato wears a jester, or fool, costume through the duration of the story. This is an example of dramatic irony because Montresor treats Fortunado like a fool because he thinks Fortunato is one, while Fortunato dresses like a fool because he thinks his is not.
I will not die of a cough.
Another example of irony is the time of year. Carnivale represents happiness and fun and excitement. The season is full of celebration. However, the opposite event occurs. Montresor murders Fortunato during Carnivale season. This is a contradiction with the setting versus the events.
No one is at the Montresor home. This is because since Montresor told them to stay, they left. This foreshadows to when Montresor did the same this is Fortunato, telling him to go back just to force him to stay.
When Montresor says, "True, true," he foreshadows to Fortunato's death, knowing exactly what he will die of. (hint: it's not a cough)
To prove he is a mason, Montresor pulls out a trowel he just happens to have on hand. This foreshadows that he is going to use it and what he will use it for.