I want revenge on Fortunato, and I need to catch him at just the right time.
Remember that his weakness is acohol.
When Montresor sees Fortunato at the carnival. Fortunato is drunk
I was going to have another friend come to test to make sure that I have amontillado.
No let me come and make sure it's amontillado and not sherry.
Gets Fortunato to come to his house by telling him that he was going to have another friend come over to test to see if the wine he had was really amontillado or just sherry.
Montresor gets Fortunato chained up
Montresor is on his last tier to closing up Fortunato forever. Since Fortunato is so drunk, he isn't fully aware of the situation, and says that him and Montresor will have a laugh about it later. But by the way the short story is written, you get the idea that Fortunato is a little aware about the fact that he probably isn't getting out since he is chains.
Montresor put in the last and final tier closing off Fortunato forever. The last thing that Montresor hears from Fortunato is the banging of his bells from his jester hat. All the alcohol and nitre had gotten to him. It's not clear if he had fallen asleep or died, but we assume that he is dead.