Spiciness: 4/5

Let's talk about the original

The original Ghost has a lot of flavor, but its design often steps on itself. For example, it can use Etherealness to pass into the Ethereal Plane (or back to the material plane). This means that, if the ghost ever appears in front of the party-- that's its whole turn! The party then has a full round to gun it down before it can do anything.

Horrifying Visage is bad as well-- AOE frightens can work well. But at the end of the day, that means you just spent your whole action to maybe frighten half the party, and all that happens is they get disadvantage on attacks against you.

The one truly powerful ability is Possession, but I'd say that's less of a combat ability, and more of an RP one-- as soon as the ghost Possesses someone, it's going to need to be exorcised (which the party may not have the gear for), so they'll likely need to put the possessed down non-lethally. I suppose you could possess one player, use that player to attack the others, and then try to repossess other players once the first is incapacitated... but with a Recharge of 6, that's unlikely to work, and probably will feel more frustrating than dangerous to your players.

To address these concerns, we turn towards a game that has fantastic ghostly warriors-- Elden Ring! That game uses no possession mechanic, but makes the combat feel unique and interesting by having the ghost fluidly appearing and disappearing from combat, being incredibly mobile and dangerous.

Cooking the Ghost, Redesigned

While the ghost has only a simple Necrotic Blade attack, it's been made far more mobile.

Now, Etherealness can be used by expending 10ft of movement-- combined with its 40 ft fly speed, it's possible to disappear, move 20 ft, and then reappear. More importantly, it's possible to appear, attack, and disappear-- meaning the party would need to ready actions to even attack it! If your party isn't comfortable with readying actions, or you think that's too strong, simply make sure you end each turn with the Ghost on the Material plane.

Ghostly Dodge has been added to make the ghost feel more dynamic, disappearing and reappearing in response to an attack. This lets you jump out of a barbarian's 5ft melee range, or dodge behind cover to block a spellcasters blast.

Horrifying Visage now uses similar wording to the Basilisk's Petrifying Gaze, requiring no action from the Ghost but allowing the players to counter it by looking away. Looking away might seem like a bad idea (since Frightened only gives disadvantage on attacks, and so does looking away), but being frightened also restricts movement, which may hinder melee characters greatly.