I've been trying to get one for a loooooong time. I've read many a guide and seen many a video, but none of them work. Is it still possible? If so, do any of y'all know of a working step-by-step

It is random- if both parents are ghosts - than the baby will always be a ghost- if one parent is a ghost there is something like a 50% chance that the baby will be a ghost. It is also dependent on who initiates woohoo-I do believe the ghost partner in the relationship initiating woohoo increases the chances of a ghost child.

How do I get a playable ghost?

So that's probably the root of your problem. In order to have a ghost baby you will first have to have either a ghost father or ghost mother. If your Sim is female you can try to seduce one of the male ghosts from the graveyard, which has become rather difficult, however, since Ambitions and the accompanying patch. And I wouldn't recommend the ghosts of Twinbrook and Barnacle Bay anyway because they have green skin and hair.
In order to have a playable ghost you will have to be good friends with a ghost and receive an opportunity call from the Science Lab called "Oh my ghost!" which allows you to bring the urn of a dead Sim there and they'll resurrect it. That's your playable ghost then.
I have also found out that it's a good idea to save before the pregnant Sim gives birth as the baby's being a ghost or not is determined at its birth.
Choose wisely though with which ghost you want to breed as some of them are very noisy

Thanks, but is there any way to force the opportunity?

Nope. Sorry, I've been wanting to do that myself.

I think you can force opportunities with one of Twallan's mods but I can't remember which one, sorry.

I found it and it works! Just click on the Grave Nraas>options...>something about a playable ghost. Thank you! For anyone else who wants it:DebugEnabler

I just recently attempted to do this for the first time and succeeded. What I did was I had my Sim raid the mausoleum for male graves (since she's female) and place them on her lot. Then each night I would wait for any ghosts to pop out and at that point I'd have her stop whatever she was doing and interact with the ghost nonstop until he left again. Finally (after maybe 3-4 nights of the ghost Sim appearing), I got their relationship high enough for them to Try for Baby and she got pregnant and gave birth to a baby girl 3 days later.
I was wondering if all ghost babies are the same or if they are influenced by the ghost that helped create them. For example, if two drowned ghosts had a baby, could their ghost baby appear to be drowned as well?

Yes, the ghost baby - if it turns out to be a ghost baby - will have the appearance of whatever ghost contributed to its making. So, let's say you have a ghost baby with the mother being an orange fire ghost and the father a blue drowning ghost there's a 50/50 chance that the baby will either be blue or orange. The ghost baby will also carry a headstone in its inventory with the plaque displaying the respective cause of death - i.e. fire or water in this case. If both parents are the same, the baby will be 100 per cent the same, too.
Another warning though, if you do not play with AwesomeMod and the NoBabyDisintegration option enabled, you must not leave a family with a ghost baby until the baby has aged up to child. This is because the game deletes all babies and toddlers of inactive families whenever all adults and teens of that household are not at home and re-adds them as soon as one of them returns. This does not work for ghost babies, however, and they will be gone for good. I guess this has got to do with the fact that technically ghost babies are considered as dead and therefore will not be re-added but sent into the netherworld. They will still show up in the family tree but you will not be able to recover them.

Thank you, I didn't know that. Can ghosts die of old age? And how long does it take a baby to age up to a kid with the shortest life span? Also, what If they're is a living sim in the house hold?

Ghosts are almost normal sims, except none of my ghosts have reached old age so i don't know if they die or not.

If a baby is born by ghosts, what colour is it?

Thanks for the info babele44! All of my sims tend to die of old age, so I guess I'd have to create some "accidents" if I want to experience different ghost babies...

Ghosts do age the same as other Sims however they do not have the option to die as do other Sims- However whenever you want them to die you click on their gravestone which should be in their personal inventory and click the"Return to Netherworld" option at this point I believe that the ghost either becomes (if a born in game or playable ghost) a NPC ghost or returns to being a NPC ghost.

Using that mod has yacked my game. I have a three sims family, all siblings. B1, G1, B2. B1 is invisible but i can make him do stuff, G1 just stands there and wont do anything i tell her too and B2 is completely fine. Any suggestions on what I should do? If I uninstall and reinstall can i still use the saves from my boinked game?

This mod has completely yacked my game. My family is made up of three sims, all siblings. B1, G1, B2. B1 is invisible but responds to my commands, G1 just stands there and wont do anything, and B2 is completely fine. Any suggestions on how to procceed? IIf i back up my saves and use them on a reinstalled game, will it turn out to be boinked too?

You can feed the Ghost you recover Ambrosia and they are alive again. I have done this a number of times, they then choose to live again or not. Some will refuse especially if they acheived their life wish while alive. They eat it and have a good meal but dont turn into a human again. The ones with a bad death should be revived in my opinion because it gives them another chance. There is a child in the current graveyard that drown, she is blue and trails water drops. She is a child and I want to have her live again to finish her life. I am trying to get Mortimer to befriend her. He is getting a job at the Science lab because he has gardening and logic to try for the opertunity. Gunther is making arrangements with Thorton Wolf for his son Ruben to start having playdates with Kristina Goth. They are just toddlers, but Gunther plans ahead. Bella and Mortimer might be taking over Greener and Greener and there might be a Wolf in Goth Manor.

Ghosts age normally unless you use a mod that disables aging for ghosts - which I do. The longer a playable ghost is out and about, so to speak, the higher the chance that you will receive a pop-up that says something like "Jane Doe is tired of this life and wishes to return to the Netherworld. Will you allow this? Yes/No." The ghost then returns into their urn and is gone. They are then again like NPC ghosts and come out from time to time to haunt your house. I don't know about the vanilla behaviour but everytime I allowed this I was nevertheless able to resurrect this ghost again. I've never seen a ghost disappear completely, yet.
And, as arelenriel said you can force a ghost to return into its NPC state by clicking on the urn in its inventory and choosing "Return to the Netherworld".

A resurrected ghost will start with its lifespan reset to the beginning of its specific lifespan.

@ WaterWolf As I said the colour of a ghost baby is determined by the colour of the ghost parent(s).

@Kestie Freehawk That's interesting because I've never had a playable ghost refuse Ambrosia. I order them to eat, they eat and they are human again. Maybe I will have to try with the horde of playable ghosts I have at the moment.
The opportunity at the Science Lab is not triggered by working at the Science Lab, BTW. Every Sim will receice this opportunity sooner or later, and most often it is triggered by experiencing the death of a family member.

@Camalus28 What I said about the deletion of ghost babies and toddlers was referring to families you do NOT play. Their ghost babies will disappear as soon as all teens and adults leave the house and go to work, school or to the park. Something you cannot prevent from happening. While your active family will have a babysitter come, inactives leave their kids behind and the game engine will remove them temporarily from the game world. Normal babies will be returned once at least one teen or adult comes back, but ghost babies will not.

You other issue belongs to the MATY forum, but in short, depending on how long AM was at work in your game save it might be difficult to get it to run in an AM free install. You won't have to reinstall, anyway, but just take it out from your Mods folder. There's also the possibility to use the "uninstall" command from within AM. Check MATY for this.

What's AM and MATY? I don't have awesomemod. I meant the DebugEnabler I talked about up there. Also, I removed the mod and it's still messed up.

Sorry, I must have skipped that post where you mentioned DebugEnabler and thought you were referring to AwesomeMod which can also enable the debug commands.
Those debug commands are rather unsafe to use and my uneducated guess is that your savegame is fucked-up now. When I used them once on a grave the resurrection was successful but the Sim disappeared and became a homeless NPC.
If you want to resurrect a ghost using the Debug commands it's probably best to use the opportunities menu and force the "Oh my Ghost" opportunity. For this you will have to click not on the grave but on the Sim you want to be the recipient of that opportunity.

Ok, Thank you. I backed up my saves before i got the mod. How do i force that opportunity? How do i access the opportunity menu?

There are three ways that I know of:
The DebugEnabler
AwesomeMod's debug interactions
MasterController

The first two unlock a debug menu that does exist in the game data and I suppose the EA developers put it there to configure the pre-made Sims in a town and for testing purposes. But as you have learned already they are unsafe to use. But within all the pie menues there is one called "opportunities" or something like that and there you can choose one that is called something like Force Ghost Opportunity.
Master Controller also has the option to force opportunities under the basic commands for a Sim. You can also use the MC to force kill a Sim and choose the cause of death.

So would the debug enabler be safe if all i used it for was forcing opportunities?

I don't know. Maybe the ones at twallan's NRaas Industries know more about the risks. I don't use this mod and AM's debuginteractions only for testing things.
I guess the safest is to install MasterController. It is a fantastic mod with lots of things in it that I cannot do without anymore. Read the manual and you'll be amazed at what it can do and it's not a core mod, i.e., you can uninstall it without causing further problems.

Is it hosted on this site? If it's not... could you possibly link it? Thanks!