I've mentioned this before when I talked about black dragons, but I'll say it again. I love lair actions and large-area effects of lairs of bad guys in D&D 5th edition. I find them very inspirational and interesting.
So I took it upon myself to add a couple to another creature I like - the Lich.
As written, the D&D lich has several lair actions, but no lair traits or regional traits Here are three of each.
A lich's lair might have any or all of the following effects in place.
• The first time a non-evil creature enters the tombs area, the creature takes 16 (3d10) necrotic damage.*
• Undead in a lich's lair have advantage against features that turn undead and on attacks against anyone who attempts to turn them or who has attempted to do so in the past hour.
• Healing magic is at disadvantage within the confines of the lich's lair.
The region around a lich's lair is warped by the creature's undead presence, causing any or all of the following effects.
• The area around a lich's lair takes on an aspect of death; grass is browned and partly withered; trees and bushes are stunted, hollowed by rot, and browned or leafless; water is ill-tasting; animals forced to stay in the area become emaciated, sickened, and unable to eat properly.
• Dead left within 6 miles of the lich's lair rot twice as fast. Buried corpses rapidly rise to the surface even if well-buried, through unnatural storms, shifting earth, or all-too-quick wind erosion.
• Skulls seem to turn and stare at anyone within 6 miles of a lich's lair, and out of the corner of one's eye they seem to glint and glow.
If the lich is destroyed, these effects end after 2d6 days.
I think those make a lich in the area a bit more entertaining. And it's easy to mistake a demi-lich's tomb for a lich's tomb, if you pay too close attention to the damaging game effects . . .
* This is identical to a demi-lich's effect, so that taking necrotic damage isn't a clue to the nature of the lich within.