One element I often see overlooked in fantasy games is the utter danger that can appear from nowhere in the dead of night and disappear completely at dawn. There are vampires sure, but most creatures are at best nocturnal and just tend not to be out during the day. One thing I try to stress in small ways in games is that everything changes when the sun goes down. When it does you may need to hole up some place until dawn breaks.
Simple rules like common undead (at least created by some means) take damage in the sunlight, or increasing the amount or types of magic that function at night, or creatures that only exist in this plane at night. A haunted castle may only appear at night, legion of the dead may flood out from the swamps and mill abound the woods. But the night is dangerous.
Often a lot of emphasis is put on terrain as a tactical consideration, but far less often is time a consideration.
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