Blood Moon is accursed occurance, happening roughly once a month, sometimes less, rarely more often.
During a Blood Moon, the lands of Hyrule are covered in crimson glow, as the Dominant Moon takes form of a Blood Moon, and thick, red dark mists, especially in areas filled with Malice or close to Maelstorm, spread across world.
The Glow of Blood Moon amplifies many dark magicks, and anyone tainted by a curse, be it Gloom or some other curse, has their afflictions worsened and multiplied, perishing many in already critical conditions. It is the most opportune time for any dark mages to cast their most powerful rituals and spells.
What’s worse, is that bodies of those perished without proper rites raise from their slumber, causing undeath mobs forming in rural areas and dark forests and great aberrations appear from the Maelstrom and huge pools of Malice.
It is also believed that those of monstrous origins go wild and mad during the moon, but this has been proven false, and any rampages caused during the night can be directed to mass hysteria, panic and oppoturnistic people. This does not stop the rumors or hysteria.

The Blood Moon lasts only a single night, after which any undeath in daylight perish and lay dormant once again, and the Aberrations of the Malice retreat back into shadows.

Due to these facts, Majority of cities have protections and rites against the Blood moons rise such as undead wards, while those in rural areas build shelters or bunkers to survive the night, while those in the wild have to fend for themselves.