Moon Phases

Moon Phases, also called Moon Cycles, are the primary progression mechanic in the story of Bloodborne.

"The red moon hangs low, and beasts rule the streets. Are we left no other choice, than to burn it all to cinders?"
-Unnamed Powder Keg

Overview

Moon phases are a mechanic by which the story of Bloodborne is visually progressed and aspects of the world altered. These cycles are thematically linked to the hunter interacting with objects and entities that alter their perception of the world, and affect gameplay, insight, quest lines, and NPCs.

Evening (1st phase)

The first Moon phase, known as 'Evening' is experienced by the hunter at the game's beginning at the start of the story of New Game+.

Visually depicted as a mid dusk setting, with an orange-black sky and low-hanging sun visible across the map.
The hunter, at this point in the night, can interact with many NPCs in their homes, typically indicated by a red lantern.
The hunter may interact with Iosefka and receive her Blood Vials at Iosefka's Clinic.

Sunset (2nd phase)

The second phase, 'Sunset' occurs when the hunter defeats Father Gascoigne and enters Oedon Chapel for the first time.

The Sun, now rapidly disappearing into the horizon, grows dim. Lighting throughout Yharnam is softer as the area takes on a darker tone.
Gilbert offers the player new dialogue in this Moon phase, and will gift the Flamesprayer to the hunter.
Iosefka, during this moon phase, will be attacked and replaced by an imposter.
All rescuable survivors can still be saved during this Moon phase.

Nightfall (3rd phase)

The penultimate Moon phase, Nightfall, is triggered when the hunter interacts with the Skull of Laurence in the Grand Cathedral after defeating Vicar Amelia.

At this point in the night, the moon becomes the primary source of light in the overworld. The sky is an inky black and the world's inhabitants will be affected in various ways by the progression of the night.
The Church Giants in Cathedral Ward will fall asleep, only to be awoken if the hunter makes too much noise near them or attacks them.
Many inhabitants of Yharnam who the hunter was previously able to hold dialogue with will begin to deteriorate as they succumb to beasthood or madness, particularly in Central Yharnam and the Cathedral Ward.
Several areas become newly available for exploration. The Forbidden Woods entrance is now accessible to the hunter, and they may also use the Cainhurst Summons to access Forsaken Castle Cainhurst.
Patches the Spider will replace the dialogue of most houses' inhabitants, luring the hunter to the Lecture Building and ultimately the Nightmare Frontier.

Blood Moon (final phase)

"When the red moon hangs low, the line between man and beast is blurred. And when the Great Ones descend, a womb will be blessed with child.
-Note found in Byrgenwerth

After defeating Rom, the Vacuous Spider, and interacting with the Woman in Bride's Dress, the Blood Moon phase is activated. In its final phase, the Moon hangs low over Yharnam and emits a deep red glow.

Most of the inhabitants of Yharnam will become non-responsive, either making grunting/hissing/growling noises or raving manically.
The kidnappers in Cathedral Ward and Yahar'gul, Unseen Village, disappear.
The sound of Mergo crying, typically requiring 60 insight to be heard, can now be heard anywhere within the world until the hunter defeats Mergo's Wet Nurse. Additionally, the Lesser Amygdala attached to the rooftops of Oedon Chapel and Yahar'Gul will be visible regardless of the hunter's insight.
The music heard in the Hunter's Dream will change permanently until the game's completion.
The player will be attacked by either Eileen the Crow or The Bloody Crow of Cainhurst (depending on their previous actions) in the Grand Cathedral.
The Grand Cathedral Lamp will become unavailable until the player confronts either Eileen or the Bloody Crow of Cainhurst.
The Hypogean Gaol Lamp will become permanently unavailable, and the area will fall silent.
The Hunter's Dream, an area that exists separately to the waking world, is unaffected by the Blood Moon until the hunter confronts Gehrman and witnesses the descent of the Moon Presence.