UNDERDARK AND MOOD
Consider what the Underdark does to your player characters’ minds. Based on each character type, what are the players feeling? Why does the NPC elf keep speaking of troubling dreams? Are the humans and hobbits feeling suffocated? Are the dwarves at home and growing resentful of the complaints? The Underdark eats at each character’s thinking. It affects sleep. They can feel the Underdark in their bones!
Your characters could encounter other one-time adventurers who have gone mad in the darkness. Ragged in their clothes, they babble, but at the same time beg to join them, beg for something cooked to eat. The madwoman healer opens her hand to reveal an albino mouse. “My best and only friend,” she claims. Could these be allies or is this yet another trap in the dangerous Underdark?
Mercy upon your characters if the lights do go out...especially if anyone ends up isolated. They will be prone to hallucinations and might even turn on each other. For humans, their emotions will run out of control. They might sing just to hear something and then burst into tears a moment later. All of this noise could attract anything.
Resources for Inspiration: