How does Poe weave images from "The Masque of the Red Death" to build the sense of hopelessness in the scene leading up to the prince's death?

Poe believed that every detail in a short story should contribute to the author's intended effect. Therefore, the sense of hopelessness leading up to and following Prince Prospero's death is actually set up from the beginning. Poe starts the story by discussing the measures the prince has taken to keep the Red Death locked out of his "extensive and magnificent structure":

A strong and lofty wall girdled it in. This wall had gates of iron. The courtiers, having entered, brought furnaces and massy hammers and welded the bolts. They resolved to leave means neither of ingress nor egress to the sudden impulses of despair or of frenzy from within. The abbey was amply provisioned. With such precautions the courtiers might bid defiance to contagion. The external world could take care of itself.

The imagery in this passage indicates the stability of the prince's hideout. Not only is the place made of iron gates, but the prince also has courtiers "weld the bolts." In making himself and his guests safe and secure within this abbey, he also, ironically, seals their fates. Once the Red Death enters this unbreachable fort, through some supernatural means, the humans inside have no chance to escape. A feeling of hopelessness pervades the ending of the story because we know from this early description that the people inside have no way to get out of this place; they are all as good as dead.
Poe's imagery throughout the story builds the ominous tone that leads to the dramatic ending. For example, he describes the black chamber and the foreboding clock that inhabits that chamber. The sound of the clock striking each hour is so disturbing that the revelers stop and momentarily feel afraid before resuming their dancing.
The image that perhaps best incapsulates the sense of hopelessness surrounding the scene of Prospero's death is the figure of the Red Death itself. The appearance of this "stranger" alone is unsettling because no one knows who he is or how he entered the property. However, the details of his figure further illustrate the horrific appearance of this unknown "guest." Poe describes this entity as

tall and gaunt, and shrouded from head to foot in the habiliments of the grave. The mask which concealed the visage was made so nearly to resemble the countenance of a stiffened corpse that the closest scrutiny must have had difficulty in detecting the cheat. And yet all this might have been endured, if not approved, by the mad revellers around. But the mummer had gone so far as to assume the type of the Red Death. His vesture was dabbled in blood—and his broad brow, with all the features of the face, was besprinkled with the scarlet horror.

The references to "the grave" and "a stiffened corpse" associate the figure with death. In addition, he is covered in blood. This passage also tells us that the party guests are not only disturbed by this appearance but also by how realistic it appears: it is as though the figure has just risen from the dead.
When Prince Prospero sees this figure, he experiences a variety of emotions, includuing "terror," "distaste," and "rage." However, the prince considers himself the authority and demands the figure be unmasked and then hung in the morning. The music has ceased, so the sound of the prince's command reverberates through the rooms. The revelers are described as frozen in shock and horror, so the Red Death makes his way through all of the chambers one by one. The prince attempts to kill the Red Death, but he ends up falling to the ground dead himself, instead. The revelers learn that there is no human figure under the mask and they are all trapped, victims to the disease they were trying to avoid by allowing themselves to be locked in by the Prince. There is no hope of escape or survival.