Montresor's instructions to his servants to stay in his mansion are an example of verbal irony because he meant for them to leave.
"I must not only punish, but punish with impunity."
An example of situational irony is Montresor's continued efforts to stop Fortunato from coming with him, which makes Fortunato want to come with him even more.
He doesn't even know.
When Montresor says, "you are luckily met," the reader knows he means that they are lucky since the carnival is an excellent time for murder, while Fortunato thinks he is happy to see him for his expertise.
Follow me to your doom.
"I must not only punish, but punish with impunity," foreshadows that Montresor will get revenge without being caught.
"It must be understood that neither by word nor by deed had I given Fortunato cause to doubt my goodwill," foreshadows that Fortunato is the one that will be punished.
"I suffered him to hurry me to my palazzo," foreshadows that Fortunato will be punished at Montresor's mansion.