There is foreshadowing when Montressor pulls out his trowel. Readers quickly know that something different is going on because most people don't keep things like a trowel in their pockets.
Fortunato is dressed in a jester-like type outfit, which looks fairly goofy and foolish. He is also fairly drunk making him a little bit unintelligent. This is also ironic because not only does he look and act like a fool, but he is a fool because he doesn't catch onto Montressors plan.
While Montressor and Fortunato are walking through the catacombs, readers get a suspicious feeling and are very intrigued. The mood is dark and errie.
"It is nothing... let us go on"
The tone is secretive, sly, witty, and serious. Montressor has some plans up his sleeve that gives the tone a slight eerieness to the story too.
"... the foot crushes a serpent rampant whose fangs are imbedded in the heel." Montressor's family motto paints readers a very clear image. The words crushed and imbedded gives readers a chance to really see it.
This is an example of Irony because Fortunato is begging to go on, but little does he know he's being played and he's begging for his own death.