I'd be interested in some examples of the monsters we'd be dealing with; it would help my character concepts.
I left it pretty vague in the OP, I know, partially to preserve the sense of mystery and party so I didn't have to come up with what the monsters might look like, but now I guess I have to stop being lazy.
The things that go bump in the night tend to be a secondary concern for your average Joe Peasant come nightfall, as they are marginally less dangerous than the more obvious threats of starvation or general civil strife. However, it can't be denied that the world becomes objectively more dangerous as the night drags on.
The usual initial beasts take the form of exaggerated version of existing creatures: packs of huge wolves with overly-pronounced features (note that 'huge' in this case means "2-3 times the size," not "a large as a building"), flocks of giant crows with razor-sharp talons, great shaggy bears with tar-black pelts, the like. While they can definitely be deadly, these sorts of creatures are usually seen as dangerous but relatively normal creatures that can be dealt with by normal means.
As the night wears on, however, things usually become more grotesque, and what was previously an annoyance becomes a true threat. The beasts, though still usually not-quite-existentially-terrifying to look upon, stop resembling existing animals, and instead take on strange variations of their own. Corpses will rise from recent graves, blind and deaf and bloated, wandering in huge packs to tear apart whatever they encounter. Phantom horsemen ride down roads, trampling anyone in their way; faceless creatures imitate men and infiltrate villages, only to carve a bloody path through them a few weeks later.
Perhaps the rarest and most dangerous situations, occurring only once or twice each night at most, are when entire armies of armored wraiths will emerge to raze and siege with no apparent goal but destruction. Protection from these phantom forces is the primary purpose of the maintenance of standing armies in the night. While the less organized monsters can be dealt with by a few skilled individuals or a talented hero, the wraith forces require mobilization and planning on a level akin to true war.
It should be understood, however, that while every night brings these monsters, they are quite rare, and though rumors of exotic and horrifying monsters travel quickly the average person will not lay eyes upon one. On the occasions that the full force of these shadowy creatures is brought to bear, such as in the mysterious demise of Varras, the results speak for themselves -- entire kingdoms can be leveled in just a few months or years.
If one is not certain whether something is a monster borne from the night or a regular beast, there are a few telltale signs: for instance, the night creatures are usually entirely silent. A wolf will howl and a soldier's blade will screech against its sheath, but all sound seems almost muted when the creatures of the night are concerned. They also leave no tracks, be that footprints or impressions in the snow or any other physical mark of movement upon the world.
There are a few traditional methods for warding off the monsters of the night. Only the most powerful, it is said, are able to withstand the heat and light of an open flame. In cases where simply holding the darkness at bay will not do, there are very few that cannot be dispatched with enough whacks by a sharp weapon.
