The elder, thirteenth and last tree of the year, is associated with death and doom.
Falling asleep under an elder tree attracts negative forces, provokes horrible nightmares and causes delirium (probably depending on the amount you had to drink to fall asleep under a tree).
In England it was considered a bad omen to burn elder wood, children in elderwood cradles would be pinched black and blue by the faeries, and some Christian legends imply that the cross upon which Christ was tortured to death was made of elderwood, and that Judas hanged himself on an elder tree.
All the same, Irish witches prefered elder broomsticks in stead of ashen ones for whatever they did with them.

The Cailleach is the Scottish winter goddess, a blue-faced crone who provides snow and violent storms, and whose reign is only broken with the coming of the spring goddess Brigit at Imbolc. At Beltane, the Cailleach returns to earth by turning to stone.
She has also a positive aspect of landscape architect: one of her creations are the Hebrides, and Ailsa Craig near the Ayrshire coast came into being when the giant Cailleach, wading through the sea with her apron full of rocks, shrieked and dropped a rock when a French sailor steered his boat underneath her and tickled her where she didn't expect it.

As a carrion-eater, the raven is often associated with death and war. Three ravens accompanied the Celtic war goddess Morrigan on the battlefield, and it was believed a raven could smell the stench of death upon someone even before he died.
In some Native American folklore, Raven is a creator and a trickster. He gave humankind sunlight, vegetation, animals, and the tides. He then wanted to marry a human woman but the men refused this. In revenge, Raven created mosquitoes to pester them to all eternity.

The Ogham sign attributed to this month is Ruis.