What are the similarities between "The Cast Of the Amontillado", "The Tell-Tale Heart", "The Masque of the Red Death"?
All three stories deal with untimely death, premature burial, and the grotesque. In Cask A man tricks a rival into a crypt and seals him alive within the walls.
The Tell-Tale Heart shows a man killing an older man (he is bothered by the man's eye) and confessing when he still hears the man's heartbeat under the floorboards.
Masque is a bit different, but there are still some threads to draw from; a prince has gathered all his loyal subjects to his castle to party and wait out the death that is sweeping the countryside. The death still comes, however, and all inside die horribly, entombed within the stone walls forever.
So, in the end, people die unnaturally in all three works.