I think in previous editions Banshee's were under a curse. Taking that an extra step have the Banshee respawn every night. To permanently kill the Banshee, either the Banshee needs to atone for the evil acts they did in life (Extremely unlikely) or find the physical remains and cast remove curse or perform a cleansing ritual.
Interesting. I'd think you'd be better off with a more flexible undead for that idea, such as a ghost or wight, as that plot might involve fighting the undead multiple times and that seems hard to pull off with the banshee (assuming you want all the fights to be interesting.) Still, I like the idea. Thank you.

9 ways to use… Beholder


1) Before running a beholder, make a chart of which PCs are the best choice of targets for eye ray 1, which are okay targets, and which are last option targets. Do it for each eye ray. It might not seem complex, but it will speed up the battle a lot.
2) Beholders are from the class of villains who talk/brag through the entire battle. Prepare a list of prepared remarks. Don’t worry about them being cheesy. Don’t respond when the players make fun of them, just go on to the next one.
3) A beholder battle consists of seeing whether the PCs can reach the beholder before it slaughters them. Once they reach it, the battle’s won. Accordingly, set up traps, obstacles, minions, or anything else to stop them from getting near. Don’t run the beholder by itself.
4) Beholders are going to be especially fond of pit traps. They can float right over them, so the traps reinforce their feelings of superiority, and provide an obstacle that doesn’t hinder them at all.
5) An ideal situation for the beholder, and a very challenging one for the players, is if they’re stuck in an area (such as a pit) where they can’t avoid the main eye ray, and with ongoing damage (acid, at the bottom of the pit.) If the beholder keeps them there, it wins.
6) You can’t choose which eye rays will fire, so any plan requires the ability to work with multiple eye rays. I used barrels of slippery oil, which it can spill with teleport, destroy with disintegrate, or unbalance (and make fall) by petrifying the right part of them.
7) If you want a trap, the beholder could have crossbows with their strings drawn back magically, or weights hanging magically from the ceiling. As soon as the beholder looks at them, the crossbows fire, and the weights drop.
8) City invasion scenario: Monsters are attacking from multiple directions, and the players have to get past them to reach the palace. Every so often, the beholder will zap their magic for a round, then hit them with eye rays as it moves elsewhere.
9) Idea for players: To defeat a beholder, shine a bright light. If forced to close its eyes, the beholder is helpless.