The dark and the night

The opposite of the light is the dusk: a dark faction of dim things (gloomlings, wisps, wraiths, fallen knights, void knights) that grow stronger toward the Ashen lands and come out in force at night. They are weak to light and resist the dark. The main arc says it plainly:

"[place] stands at the edge of the dusk."

"[rival] gather at [other]. This is where the dusk makes its stand."

The night

3 creatures only appear at night (Hollow Wisp, Bog Wraith, Night Terror). Dark creatures spawn at 1.5 times the weight at night. A torch lights the dark and never burns out; a fire is a small sun. The tutorial puts it in one line: Night belongs to the Dark. Go back to your fire with the torch in your hand and wait for dusk. A bed with every player in it skips the night.

Dark weathers (Voidmist surge, Ash storm) make dark creatures hit 20% harder; storms muffle hearing, which helps a hiding player.

Raids: the Dusk Tides

Each boss kill sets a world key, and the key arms the raid of the same tier. The dark assaults a settlement or the player base in waves:

The hosts of the dark

Dark magic

The Umbra school is dark magic: Shadowstep, Drain Essence, Veil of Night, Umbral Brand. Casting it raises Corruption (a world modifier can turn this off). The dark clans stand in the dark half of the alignment scale; the dusk border is where the main arc ends.

Seven lords

Each tier has one boss, and the last is the Mother of Dimming: