A Gothic protagonist - Protagonist is isolated & has no friends
Emotions Run High - Defying their own common sense
"Within the wall thus exposed by the displacing of the bones, we perceived a still interior crypt or recess... for no especial use..." (page 5) the grave that Montressor uses for Fortunato.
"You are rich, respected, admired, beloved; as I once was." (page 3) This shows that he is alone and has no friends.
Some sort of Decay
"He was too much astounded to resist." (page 5) This shows that Fortunado is gullible and defying his own common sense.
"As I said these words I busied myself among the pile of bones of which I have before spoken." (page 5) This shows what unlucky omen appears.
"One evening during the supreme madness of the carnival season." (page 1) "Into the inmost recesses of the catacombs." (page 4) These settings show how the story ends up going downhill and began a decay.
"I discovered that the intoxication of Fortunato had in a great measure worn off... It was not a cry of a drunken man." (page 6) People don't just sober up in 1 minute.