So I'm trying to apply some NBT data to any of a specific entity that join the world. In-game the command /summon primitivemobs:mother_spider ~ ~ ~ {ForgeData:{InfernalMobsMod:"Ninja Webber Darkness"}} will work as expected, summoning a mother spider with the above forge data, but this doesn't work in spawn.json:
[ { "mob": "primitivemobs:mother_spider", "result": "default", "onjoin": true, "healthmultiply": 2, "damagemultiply": 2, "speedmultiply": 1.2, "nbt": { "ForgeData": { "InfernalMobsMod":"Ninja Webber Darkness" } } } ]
I have tried a variety of different combinations of curly braces and quotes, all of which end up either being invalid json, or just not doing anything. The console doesn't output any errors relating to incontrol as far as I can see.

mm the code tag seems to remove line breaks. might be more readable this way: https://pastebin.com/ZvYLTy83