The Changing Manor appearance changes with each owner he had, even if he always keeps gothic elements to its general architecture... When the Manor looks for a new owner, it usually appears as an old metal key in the material plan surroundings where the previous owner passed away. If a new potential owner touch the key, he will soon see a talking Raven, and be invited to follow the creature up to a strange passage. Going through the passage will finalize the attunement. The key casts the Magnificent Mansion spell once and disappears to become a permanent contract owned by the Manor's spirit in an unknown place.

The Manor is always invisible outside its location in the Astral Sea (and maybe Sigil). When you access it, you directly appear inside through one of its numerous doors or at its entrance gate in the front garden (see below).

If the Manor's origin are mysterious and ancient, the extremely rare information on its subject indicate it would have been created on Sigil, the city of doors, by an obscure Archmage whose name has been long forgotten. The original manor would have been destroyed through an "unlucky" experiment and its ruins, considered as cursed, would have been left untouched somewhere in the Lady's Ward. Gifted with consciousness during this incident, the magical habitation would have escaped its fate somehow, creating its own demi plane to survive in a hidden location nearby or within the Astral Sea.

In any case, the reality of the Changing Manor is that it is filled with numerous doors that connect to various plans of existence and even to the Cage itself. Once attuned to its magical key, its owner can communicate, telepathically or verbally, with the Manor consciousness, that only appears as a ghostly servant looking like Edgar Allan Poe or as a talking Raven. He will also benefit from the various capacities of the place, that he will need to progressively discover and unlocked, and be affected by its curse.

About the Manor:

• It fundamentally is a Magnificent Mansion spell that gained permanent consciousness and has gone rogue. Each time the Manor has a new owner, it creates a new Magnificent Mansion space with its unique rooms etc. connected to the previous ones already created. The number of previous owners is unknown and up to the DM to decide. 
• Once a new owner takes possession of the Manor, he creates his own part of the mansion that he can control. He has no control over the connections to the previously created areas, and neither on those areas themselves. The look and feel of those other mansion can't be changed from how they were originally designed.
• As a part of the Manor's curse, each Mansion created has trapped the soul of its owner when he died. Some of them were good and some were bad... Therefore, those spaces, once discovered, can be filled with dangerous creatures and elements, illusory if they had been freshly created but gaining a ghostly substance over time.
• The number of Rooms inside the manor is potentially infinite. Within the space that has been created and after discovered by its new owner, it provides any advantages he would normally benefit from with the Magnificent Mansion spell... he just needs to think about it or to decrypt the rules that apply in previsouly created areas.
• The owner can also store real items inside as the Manor never vanishes, but items created in the Manor through the means of the Magnificent Mansion spell will disappear if taken outside.
• Last but not least, the owner controls the time flow in the Manor vs the plane he was last accessed from and can perceive anything that happens or has happened inside the discovered rooms through a variation of scrying that scan the present as the past. The Manor's spirit always knows everything that happens or has happened inside (even in the rooms not yet discovered, but he would never talk about it as it would be rude).

 About the Manor's abilities:

• The manor's owner has advantage on Death Saving throws, as long as he takes his long rests in the Manor (see the Manor's curse for more details).
• He is also hidden from divination magic as fundamentally a part of his essence is not really there. He can't be targeted by such magic or perceived through magical scrying sensors.
• Each time he leaves the Manor, he also benefits from a familiar that is always a Raven, as described in the find familiar.
  • This Raven is a manifestation of the Manor's spirit, he can talk verbally or telepathically.
  • He is immune to non-magical damages and if he gets destroyed he automatically comes back the next day, at dawn, if the Manor's owner is not in the Manor.
• Last but not least, the owner can create a passage to get back to the Manor. It essentially translates in 2 specific abilities for him:
  • Those functionalities are at will, BUT each extra use after the first one will cause 1 level of exhaustion.
  • teleport. Except if the owner is using this ability to move to a nearby location (500 feet or so), he first needs to find the access to the far away location he is looking for, if it exists, through the different Manor's segments, therefore explore the Mansion.
  • plane shift. The owner also needs to find the plane access, if it exists, through the Manor's segments, therefore explore the Mansion.

About the Manor's curse:

• The Changing Manor is a cursed item.
  • The Manor's spirit focuses on its own survival and does so by nourishing on his owner's life essence and by keep expending,
  • Therefore, by the presence of his owners in its walls and by their death. That being said, he will never directly attempt to his owner's life.
• If the owner does not come back to the manor once every 24 hours, he suffers from 1 point of exhaustion (cumulative) that he will only regain by spending a long rest in the Manor.
• If the owner does not take a long rest in the Manor once every 24 hours, he loses his advantage against death saving throws. He gets the advantage back once he spends a long rest in the Manor again.
• If the Manor owner dies, any spell to revive him requires a death saving throw to succeed (without advantage).
  • If he fails, he can still be raised from the dead, but it will cost him 1d4 wisdom points as a part of his essence will remain in the Manor.
  • As long as he stays within the manor's walls, his wisdom is full and unaffected. As soon as he leaves its walls, he needs to remove those points from its effective wisdom.
  • If at some point the owner wisdom falls to 0, he can't be revived any more. He becomes a ghost at the service of the Manor's spirit who will be looking for a new owner.
• In addition, outside the initial area created by a new owner, the Manor is a dangerous place that needs to be explored. When such exploration happens, it is up to the DM to populate those other areas and to generate the encounters he wants. Those can be beneficial, but it is rarely the case as a new owner would most likely be perceived by the previous owner's dead spirit as a trespasser. 
  • The Manor's spirit will always protect the actual owner from such dangers in the space he initially created (or he ends-up discovering and conquering) and eventually warns him of some dangers when exploring based on its relationship with him.
  • That being said, he will not do such things with guests and could easily manipulate a curious one so he ends-up in a dangerous place by opening the wrong door.
• The only way to transfer ownership is to die and not be raised from the dead (or not being able to be raised anymore) or to willingly transfer it after someone has removed the curse first.

About the Manor as a sentient item:

• The Manor's spirit is as polite as a royal house's servant, it is witty, educated, full of irony and a bit of a dashing smart ass. That being said, he is also malicious and if he will never mean any harm to its owner, he only tolerates its master's guests and has no issue putting them into dangerous situations within its walls... After all, their essence is some kind of food for him...
• Intelligence: 15, Wisdom: 15, Charisma: 10
• Able to communicate verbally or telepathically in different languages (in the Manor only or through the Raven form)
• Hearing and darkvision 120 feet
• Alignment: CN
• Purpose: Survivor

Notes: Advantage: Death Saving Throws, Exhaustion