From The Depths Mod 1.12.2 (Summon Any Monster in the Game)

The recipe file is how you can go about and create an item in the world in which to summon your boss.

These recipes are loaded during minecraft startup. If you want to update a recipe you must restart the game in order for your changes to be used.

Each recipe must be in their own file. They use the same layout as Minecraft’s JSON file recipes that modders use. The important part is the recipe result. The item must always be the totem of summoning with NBT data containing the entityKey which matches the “key” property in the spawnInfo.json file.

Note: If you don’t see your recipe in JEI, please check the log for an error loading a recipe. There is probably a syntax problem with the JSON and this error message should tell you what is wrong. It will typically complain about malformed JSON.

Important Note: While we are using Minecraft’s JSON file recipe loader, we do not support things such as _constant.json, _factories.json or condition files.

{ "type": "minecraft:crafting_shaped", "group": "Summon", "pattern": [ "aaa", "aaa", "aaa" ], "key": { "a": { "item": "minecraft:cobblestone" } }, "result": { "item": "from_the_depths:item_totem_of_summoning", "data": 0, "nbt": { "entityInfo": { "entityKey": "Zombie" } }, "count": 1 }
}

Source