Have her pass through walls, knock over bureaus on them, etc.ДЄction: Throw item, +5 to hit.

In fact, I'd start the encounter as soon as they enter the orphanage. Let's give her a legendary action, and a reaction, and mix in some poltergeist behavior.ДЄction: As an action, the banshee can become invisible. Either their ears are blocked so they can't hear the banshee screams, or they aren't.ДЄlso, let's give the banshee some interesting things to do. I'm sure they'll give you that argument of, 'Well, I can hear some stuff, it's just muffled' - don't take that. Toss one of these in: ДЄlso, don't forget that, if their ears are blocked, they can't hear anything. Well, an orphanage has lots of kids toys around. I want this to be a hard fight, something I have found hard with the amount of damage my party does.

If someone standing on the edge of the fight is grabbed by a shadow the others may not notice. My thought is that as the PCs will have their ears completely blocked, they are disadvantaged through not being able to communicate easily to each other. I was thinking about adding some extra health from 58 to 80ish, increasing the save DC on horrifying visage from 13 to 14 and adding 3 (ish) shadows into the fray. So to make things a bit harder, and to make sure my players come out feeling like heroes, I need to find a way to increase the difficulty and I was hoping you guys could give some pointers!

Due to some impressive researching they were able to find out about the banshees scream and are planning on blocking their ears which although is great for them, makes the banshee way easier than the story deserves (in my opinion). They are coming to the end of a little storyline and will be facing a banshee in the basement of an orphanage. Playing a 5e campaign, DMing 6 lvl 4 players.

Banshee d&d 5e