This guide assumes you are using my (Fexty) Quest Editor + Spawn Editor.

Custom spawns are files separate from the quest files. Each spawn file can contain any number of spawns, for one specific map. Each spawn in the file can be used for all monsters, and can optionally be locked to a specific Quest ID. (Only a single one for now, may or may not increase this in the future.)

Spawn files belong in reframework/quests/spawn/stage, and can be called whatever you want, just like quest files.

You can create a new spawn file via File > New. After that simply select the map, add any number of Setters, give each one a unique name, and match the Set Name inside the quest accordingly.

The Area and Subspawn properties don't actually have any effect on how the spawn behaves, they are simply identifiers. So if you're making a new spawn, make sure they're unique. For example if your spawn is going to be in Area 5, set area to 5, and Subspawn to something like 20.

That's only a suggestion from me tho, thechnically you can just set it to whatever you want, as long as it doesn't interfere with an existing ID. (So e.g. having Area as 214324 and Subspawn as 904137 is totally valid.)

Then select the "Has Coordinates" checkbox, and enter the desired coordinates. If you want to pick coordinates from one of the existing spawns, you can get them from the Edit menu, via Edit > Insert Coordinates > <Map>.

Let's say you want to add a custom spawn for Goss Harag (or any monster) in the Sandy Plains, Area 5.

1. Open the editor, and create a new file with File > New. I will call it SandyPlains.json.
2. Select the map to be Sandy Plains.
3. Click on "Add Setter", and select it from the "Setter" dropdown menu.
4. Now change the "Set Name" to something like "Area 5 Default". Remember this, as you'll need it later.
5. Now select Spawn A from the dropdown
6. I only want a single possibly spawn here, so I'm going to set the "Spawn Chance" to 100, but you can set it so 60 for example if you want multiple possible subspawns.
7. Now change the "Spawn Area" to 5 (or whatever you want), and the "Sub Spawn" to anything above 2. I'm going to set it to 3.
8. Since I don't want to go extract coordinates myself from the game, I am going to paste in an existing set of coordinates. To do this I select Edit > Insert Coordinates > Sandy Plains > Area 5 [Sub 0].
9. Finally hit Ctrl+S to save the file.
10. Now open your Goss Harag (or whatever) quest in the quest editor, find the Monster entry for the monster you want to spawn in the sandy plains, and change the "Set Name" to whatever you decided on in the spawn editor. For me that's "Area 5 Default".
11. Finally save your quest file and start the game.