It would be nice to include some basic rules for aging effects based on stages like middle aged, old, venerable. And also how fast the character dies after exceeding max age for that race. It might be fun to allow a count down in hours based on current CON score and requiring Death Saves every hour. This gives a little time to find a priest high enough level to perform Greater Restoration. Great role playing oportunity during this slow path to twilight. 

Is it only failing the initial saving throw by 5 or more that causes the aging effect, or does each subsequent roll (until the roll succeeds or the effect expires) failing by 5 or more age them further?

I read it as only the first save. They tend to be quite deliberate in their phrasing, including the order that effects are listed in.

So what about the ghost of a former knight of great martial prowess, what about the ghost of the orc barbarian warlord, what about the ghost of the royal assassin? They cant use their class abilities of their former glory? What about the archmage ghost, he cant use his knowledge to cast spells now that he finally controls a body for the somatic components? Why cant the ghost possess a monkey, or a dog, cat or horse for that matter?

Who says you can't?

That's what custom NPCs and monsters are for.

It says the challenge rating is 4.  That means that an appropriately equipped and well-rested party of four 4th-level adventurers should be able to defeat a ghost without suffering any casualties?  Therefore, this wouldn't be appropriate for a group of four or five 1st-level characters?

Quote from Radames >>

It says the challenge rating is 4.  That means that an appropriately equipped and well-rested party of four 4th-level adventurers should be able to defeat a ghost without suffering any casualties?  Therefore, this wouldn't be appropriate for a group of four or five 1st-level characters?

A fair assumption, but CR ratings are imperfect, and incorporeal undead tend to punch well above their weight.  I’d say even if you wanted to use these for a really deadly encounter, you’d still want to save it until the PCs are  2nd (or even 3rd) level characters.

Just, looking at the average damage output alone, it would KO any 1st level PC in a single hit, each.  Also, PCs that low level are less likely to have the resources to get past its resistances.

if you’re looking for something to challenge a first level party, I would suggest a specter.

i know it has a much lower CR, but it’s actually pretty tough. Even more so if you add some vermin or lesser undead to assist it.

Quote from Dr_Frederick >>

Quote from Radames >>

It says the challenge rating is 4.  That means that an appropriately equipped and well-rested party of four 4th-level adventurers should be able to defeat a ghost without suffering any casualties?  Therefore, this wouldn't be appropriate for a group of four or five 1st-level characters?

 

A fair assumption, but CR ratings are imperfect, and incorporeal undead tend to punch well above their weight.  I’d say even if you wanted to use these for a really deadly encounter, you’d still want to save it until the PCs are  2nd (or even 3rd) level characters.

Just, looking at the average damage output alone, it would KO any 1st level PC in a single hit, each.  Also, PCs that low level are less likely to have the resources to get past its resistances.

if you’re looking for something to challenge a first level party, I would suggest a specter.

i know it has a much lower CR, but it’s actually pretty tough. Even more so if you add some vermin or lesser undead to assist it.

 I would definitely suggest specters, possibly giving them a greatsword of some other weapon to increase coolness.

I agree, can definitely pack quite a punch. One of those monsters that will utterly destroy a party with but a few unlucky dice rolls. The ghost I ran nearly killed two members of the 7-8th level party.

Damage resistance to non magical, not immunity? So you can technically beat a non corporeal creature to death with a barstool...that’s broken. Werewolves have immunity to nonmagical weapons but ethereal undead only have resistance. Somebody didn’t think that through...

 Now I'm imagining a barbarian beating a ghost to death with a bar stool. XD

What if you are a ghost

Quote from Beastmode360768 >>

What if you are a ghost

 

You mean like a Ghost PC?  That’s a great question.

The simplest option is to just hand a player the statblock above, although I do not recommend that unless the party is quite high level (above 8th level).

If you care a lot about balance, and proper mechanics, I recommend looking at the undead race options in Unearthed Arcana.  You may want to tweak them a bit, but they should give you a good base to work off of.

If you are looking to make an existing PC into a ghosts, and can’t be bothered with exact balancing (like for a one-shot or some such), I’d suggest just taking the PC as it is now, and slapping on a few of the key traits that ghosts share with wraiths and specters:  Incorporeal Movement, a hover speed, and maybe the damage resistances/immunities (if you really don’t care much about balance).

This monster is a perfect candidate for home-brewed Lair Actions.  Perhaps, Legendary Actions as well.

If you give the ghost abilities that function, while it’s sitting on the Ethereal Plane, you could begin the encounter with an interesting “haunting” phase, where the party has to figure out how  to draw the ghost into a confrontation on the Material.

Of course, that would also up the difficulty of an already difficult encounter, so take this suggestion with a grain of salt.

How do people handle "class features" when a ghost possesses a city NPC?

For example, a Champion gets 3 attacks with Multiattack. I would consider this a class feature of the Fighter class.

But others could say that NPCs have similar powers, but are not player classes. In that case, a ghost-possessed Champion should be able to do Multiattack, Second Wind, and Indomitable.

If I were DM'ing it, I would say that only its initial failed save within that 24 hour window would age it. If they ran into the thing again the next day, however, the party may have to look into finding convalescent care for senile adventurers.

Quote from Quasimodal >>

How do people handle "class features" when a ghost possesses a city NPC?

For example, a Champion gets 3 attacks with Multiattack. I would consider this a class feature of the Fighter class.

But others could say that NPCs have similar powers, but are not player classes. In that case, a ghost-possessed Champion should be able to do Multiattack, Second Wind, and Indomitable.

It says the ghost doesn't gain the knowledge of the victim, so it wouldn't suddenly know how to do that. However, I would rule that it could level up while inside the creature. 

Aarakocra can get instakilled by this.

" If a target's saving throw is successful or the effect ends for it, the target is immune to this ghost's Horrifying Visage for the next 24 hours. "

And what plausible mythos is the aging  based on? How can a ghost have a standard fear ability yet that isn't alloted to any basic spook, aberration, or demon? Essentially permanent possession? How many kings, queens, nobles are possessed by ghosts daily with no access to an exorcist? Sometimes I'm glad to see the death spiral that is dnd writing after curse of dracula rip-off.