"we will go back; your health is precious. You are rich, respected, admired, beloved; you are happy, as once I was. You are a man to be missed. For me it is no matter. We will go back; you will be ill, and I cannot be responsible. Besides, there is Luchresi --
"I had told them that I should not return until the morning, and had given them explicit orders not to stir from the house. These orders were sufficient, I well knew, to insure their immediate disappearance, one and all, as soon as my back was turned."
I continued, as was my in to smile in his face, and he did not perceive that my to smile now was at the thought of his immolation.
This is ironic for this is the exact opposite from what are narrator wants, and that is his death.
At length I would be avenged; I must not only punish but punish with impunity.
This is situationally ironic for you would expect servants to do as they're told, but as we can see that is not the truth.
"Enough, the cough's a mere nothing; it will not kill me. I shall not die of a cough."
this shows that Fortunato is unaware of his malicious smile, not a kind one
"It is this," I answered, producing from beneath the folds of my roquelaire a trowel.
This was in Montresor mind as he manipulated him to the wine catacombs.
This is foreshadowing that yes, he shall not die of his cough, but it is maliciously inferring that he will die of something else.
When Montresor produced a trowel, it is a indication of his fate, when later on he will get walled in by the very tool that seals his fate.