Prince Prospero- Outwith was the Red Death (A, Support): The weapon of choice and first Noble Phantasm of Assassin is the knife wielded by the Prince Prospero, who hid within a fortified Abbey and disregarded his domains, in an attempt to strike Assassin down. In itself the knife is a regular weapon for a Servant, the only special properties being held is its ability to deal regular damage to Servants. The dagger symbolises how difficult it is for human power to defeat the Red Death and to fully rid themselves of their human frailty. While holding the dagger Assassin could be described as Ethereal or Intangible. Almost all attacks will pass through Assassin harmlessly, a strong defence against conventional human weaponry. Though Thaumaturgy could potentially have some effect on Assassin it would have to be highly complex and specialised in cleansing, the removal of disease or another trait. However, Noble Phantasms and weapons with high Mystery can potentially harm Assassin, though if they do not have cleansing or other traits they will deal significantly reduced damage.
And Darkness and Decay and the Red Death held illimitable dominion over all.- And now was acknowledged the presence of the Red Death (B, Anti-Army): A complex bounded field projected from Assassin it is the true method of killing used by this Servant. In its most basic state an area of a 1.8 meters radius around Assassin is affected, entering into this zone will quickly begin to drain the Strength of the unfortunates who have come into Assassins presence, a prolonged stay within the Noble Phantasm will reveal that the world begins to darken, as if all was an inky, velvet black, and Assassin becomes more and more vividly red. The blood of the victim will pour out through the pours and sharp pains and dizziness will accompany the quick death of any human to enter Assassins dominion. Resistance against this Noble Phantasm is provided by being separate from humanity, in other words Heroic Spirits have some protection in regards to this. Those who have particularly high Endurance or another trait such as Divinity that marks their distinction from humanity will be more difficult targets but ultimately physical contact with Assassin can prove fatal to almost all.
This is, of course, the inert state of Assassin's Noble Phantasm. Upon entering into a sealed, fortified or otherwise secure building Assassin can activate the Noble Phantasm at its fullest capacity, though it does require a constant supply of Mana it does not drain Assassin quickly and in theory with an expert Master this Noble Phantasm could be permanent.
As long as Assassin remains within the building it is transformed by the Bounded Field into the fortified Abbey of Prince Prospero. Exit by any bar Assassin is quite difficult as of course only it can end the Noble Phantasm, with the exception of escape oriented Noble Phantasms, Reality Marbles or skills relating to escape. Those observing the location being used by Assassin will see no external change but upon entering will find themselves within the Abbey with almost no chance of escape.
The Abbey is divided into seven types of "room", vast imperial suites of a grand fashion they are more or less similar with one exception. They are referred to by colour, beginning with blue and then progressing through purple, green, orange, white, violet and then finally black. Those entering find themselves in the violet room and on the edge of the oppressive black room. It is possible to see from one room into all the others either through the apertures where doors may be expected or through the large stained glass windows. In each room the windows reflect the colour of that room save for the black room which we shall come to later for it is of the most importance. Of other mention is that each room is ornamented as if for a large gathering, with the exception of the black room, and that attempts to understand the topography or architecture of the Abbey is difficult as, unlike Poe's description, it defies Euclidean understanding, however the black room could be described as the "innermost" room.
Within the black room there is no ornamentation but large and blank black tapestries of velvet that cover the walls and roof of the room, however there is a large and ostentatious ebony clock against a wall that always seems to be in direct sight of those looking into the room, when the bell tolls the hour only those who have some kind of Mental Interference denying skill can attempt to stop their body from being halted in its movements for at least a period of 10 to 20 minutes. Bravery or Mental Pollution to name a few at B rank aid in defying the clocks influence.
Those who are unfortunate enough to enter the Abbey begin in the violet room on the threshold of the black room, while Assassin is positioned in the center of the black "velvet" room itself. The effect of the Noble Phantasm is an amplification of its original qualities, in the outermost room, blue, the Strength will be slowly sapped away from the foes who do not possess Endurance of Rank C or higher, and to move (or be moved) closer to the central room, black, begins to take its toll. Within the black room itself the symptoms of the Red Death, as previously described, are manifest on those who do not posses A+ Endurance or some great distance from Mankind. Physical contact with Assassin is all but certain death unless Endurance of EX Rank is possessed or a complete separation from Mankind is distinct within the victims.
Now with regard to Assassin it is the movements of this Servant which define the topography of the entire Abbey, where Assassin moves is now the center of the black room and the entire Abbey seamlessly is molded around this. Now those who have been trapped by this Noble Phantasm will not be affected as smoothly as the Abbey itself, if Assassin were to move towards them they would be moved towards the black room, and if it were to move away they would find themselves closer to the blue room (of course, until the outermost wall is reached). This leaves the victims of this Noble Phantasm who cannot survive to do battle with Assassin with the meager hope that they can outrun the somewhat slow Servant and wait until the Noble Phantasm collapses due to a lack of Mana on Assassins part. However the constant tolling of the bell can hamper this plan somewhat.