Liminal deity

A liminal deity is a god or goddess in mythology who presides over thresholds, gates, or doorways; "a crosser of boundaries".

[1] These gods are believed to oversee a state of transition of some kind; such as, the old to the new, the unconscious to the conscious state, the familiar to the unknown.

[2] Types of liminal deities include dying-and-rising deities, various agricultural deities, psychopomps and those who descend into the underworld: crossing the threshold between life and death.

Vegetation deities mimic the annual dying and returning of plant life, making them seasonally cyclical liminal deities in contrast to the one-time journey typical of the dying-and-rising myth.

[3] Liminality is a term given currency in the twentieth century by British cultural anthropologist Victor Turner.

Janus was believed to see over times of change, such as the New Year and the beginning of the day.
Mercury was a god of travellers, like his Greek equivalent Hermes.
Jangseung are traditionally placed at the boundaries of villages
Christians believe Jesus crossed the boundary from the afterlife to earth during his resurrection.