Future Press game guide description: "A soulless automaton residing in the Hunter's Dream, the doll's purpose is to care for new hunters and embolden their flesh with the power of blood echoes. Due to her lack of human emotion, it can be difficult to tell what she's thinking; she isn't one for frivolous conversation, but will occasionally share profound musings when you speak to her over the course of the game. Her aloof and sometimes coy disposition tends to give the impression that she knows more than she's willing to divulge, but in reality she is quite naive and her knowledge of the world outside the dream comes only from the stories shared with her by past hunters."
The Plain Doll resides in the Hunter's Dream and is able to channel your Blood Echoes into strength. It was created at The Workshop with meticulous care, by a hunter with a “mania”. The creator of the Doll may have created it to be their unfaltering friend, which indicates that they were very lonely. In the Waking World the Plain Doll can be seen on the floor of the Abandoned Workshop, propped up against a wall. One of the fingers on its hand is twitching intermittently, a gesture that the Doll can be seen doing when found sleeping in the Hunter's Dream. Next to the Doll's body in the Abandoned Workshop is an altar with a One Third Umbilical Cord on it. This particular One Third Umbilical Cord “precipitated the encounter with the pale moon, which beckoned the Hunters and conceived the Hunter's Dream.”
The Doll tells you that she is in the dream “to look after you.” She does this by channeling the player's blood echoes into strength. When she does this the Hunter must stand close, and shut their eyes. She will position her hands on either side of the Hunter's upturned palm and an energy can be seen radiating around the hunter's hand. The Doll has evidently been assisting hunters for a long time, as she will tell you that countless hunters have visited the Hunter's Dream. We know that both Eileen and Djura have been to the Dream because of their dialogue. When a Hunter returns to the waking world by submitting to death in the Hunter's Dream at Gehrman's hand, a tombstone is created in the Hunter's Dream, which the Doll occasionally visits.
When not assisting the player the doll will sometimes be found sleeping, sometimes kneeling before the grave that gives the player access to the Hunter's Nightmare and sometimes praying to the Moon Presence, and the Messengers on the Hunter's behalf. The Doll evidently thinks, and is not just an automated creature. She will ask the Player about the gods and their love and tell them how she has changed after Lady Maria has been defeated. She will also feel emotions under immediate circumstances. She expresses love for the player and her creator, and will shed a tear when the Small Hair Ornament is given to her.
The Doll is also aware of the nature of the player's blood. She will comment that she can sense the “ancient echoes” in the player's blood after they have defeated Rom and that these echoes soothe her.
When attacked, the Doll's blood is white. It is not the pale amber-yellow color of serum which is found in the Kin enemies, nor the red color of blood found in the other enemies of the game, including the Great Ones, but a unique white. The only other blood like this appears around the Messengers when they bubble up from the ground at a lamp post, message, bath or tombstone. When the Doll is killed, the player will still be able to channel their blood echoes in the spot where she usually stands. Upon returning to the Hunter's Dream, the Doll will be alive and well, standing in the same spot and will greet the player as if they were meeting for the first time by explaining her purpose.
If the player chooses to have their life ended by Gehrman, the Doll will wish them farewell, and pray at their tombstone. If the player decides to fight Gehrman but cannot overcome the Moon Presence, the Doll will be the one to take care of the Player as they assume Gehrman's role. If the player ascends to become a Great One, the Doll will be the one to take care of them, like a mother would.
The Tear Stone description states that a doll sheds neither blood nor tears, and thus its nature remains unknown. The Plain Doll sheds both blood and tears, implying that its nature can be known. This description indicates that the Doll is not simply a Doll, though the vessel in the Abandoned Workshop may be just that, the Doll players encounter in the Hunter's Dream may be anything but.