Okay, so, after roughly 80 hours of freakingly boring goblin grinding, I've finally leveled all jobs for all characters to 99.
Gonna be honest, Jack of all Trades is an absolutely inhuman task, if you don't have a second screen to watch some stuff while grinding, and still one of the most stupid and idiotic achievements in existence, even if you DO own one.
As such, I decided to spare you guys the process and just provide my save file.

Yes, there are guides on how to cheat this with some shady cheat engines.
There are guides on how to activate makros, which do the task without your input - but still requiring more than a 100 hours of the game running in the background.

And there is this magnificent guide, which I used to do it legitimately. Please open it to leave a thumbs up, it was truly helpful to me.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=274741499
But even so, Jack of All Trades is just plain stupid. Personally, I consider it a straight insult to achievement hunters. Therefor, you'll find several sources for my save file below.
Do yourself a favor and do something useful with your time.
This achievement is no challenge to overcome. It's a waste of time.

Sorry to all people, who already unlocked this the fair way. I know, my save file kinda devalueates the time you spend on grinding the achievement yourself.
But I don't want anyone else to suffer through this, as I did.

First of all, I do NOT know, if this works for Mac and Linux!
I've confirmed it for Windows, but I don't guarantee anything for the other operating systems.

And I know that downloading stuff from the internet can be a doubtful thing. So I'll just provide a few sources, from which you can pull the save file. Choose one you have experience with, and which you can trust:


Google Drive:
https://drive.google.com/drive/folders/11erhNA1Qm_M0t2PzKv1BpHBOYiTvSafH?usp=sharing

DropBox (requires account):
https://www.dropbox.com/sh/3pq4sh4sijjbfhn/AAABT2y26k6_PJ1mTrZYmqN6a?dl=0

NexusMods (requires account):
https://www.nexusmods.com/finalfantasy3/mods/5


In there you're gonna find a SAVE.BIN, or a .zip containing the save, if you should prefer that.
In order to load it, you need to do 2 things:

1) Steam Library -> Final Fantasy III -> click right mouse button ->
Properties... -> "Updates" tab -> REMOVE the toggle from "Enable Steam Cloud synchronization"

2) Open your windows explorer and navigate to:
C:\Users\ [YourUserName] \AppData\Local\FF3_Win32
In there you're gonna find a directory/folder with a random combination of numbers.
(In my case it's 76561198379269885). Leave that one as it is and open it.

Now, this one is important: Backup your current save file, if you still have achievements to unlock, except for all job levels and 100% bestiary!
I've taken some precautions to lock you out of most other endgame achievements!
Those other achievements have fair requirements. So no help from me.

Once you've copied your own save file to another folder, you may replace it with the one I provided.

Start the game.
All 3 slots within that save are identical to each other.
Choose whichever you want or just click "Continue"

3 of the 4 characters have all jobs on level 99. The last one, Luneth, is missing exactly 1 action to get there himself, thus unlocking you the achievement. All you gotta do is to engage in a single fight.
Order Luneth to "Attack" and the other 3 to "Guard" and you're done.

After the fight, you'll unlock:

Jack of All Trades
Attain level 99 with all jobs for all characters.


Filling Up the Grotesquerie
Complete the entire Bestiary.



I hadn't exactly planned to provide a save for the Bestiary. It just happened.
But it's also missable and would take several dozen hours to do again, so... I'll just leave it as it is.