How to code a custom spawn egg.

When you create a mob it automatically creates a spawn egg

just check if the make this mob a boss with a bossbar is checked

This is simply done by code editing: I'll walk you thru it step by step.

1st: Create a living entity and make sure the spawning egg is checked

2nd: Create a recipe using the recipe design you want. For the output, just pick any other spawn egg (like turtle)
 

Now for the complicated part:

3rd:Edit the recipe code directily, this is done by selecting the left icon below the green + sign, look for "Edit code for selected mod element"

4th: Once you done it, it will open a new tab on mcreator with a .json file, now this is where you replace the turtle egg with your custom mob egg. There are 2 things to replace, first is the mod group, 2nd is the egg:

It should look like this:
the "group" and "item from key" is automatically set by mcreator to the ones you set on step 2, the thing you just need to edit is on this is the result - items.

By default, a turtle egg will have it like this: minecraft:turtle_spawn_egg
just replace the word minecraft with your groupname and the turtle_spawn_egg with your custom mob egg. Dont delete the : (colon) between them

To get your spawn egg code btw, just edit your living entity mob (Similar to step 3 but instead click the .java and not the renderer)

5th: save it and lock the code. Locking is needed or else mcreator wont save your changes, run the game and try it out ingame.

{
  "group": "YOURMODGROUPNAMEHERE",
  "type": "minecraft:crafting_shaped",
  "pattern": [
    "01",
    " 3"
  ],
  "key": {
    "0": {
      "item": "SOMERECIPEITEMHERE"
    },
    "1": {
      "item": "SOMERECIPEITEMHERE"
    },
    "3": {
      "item": "SOMERECIPEITEMHERE"
    }
  },
  "result": {
    "item": "YOURMODGROUPNAMEHERE:YOURCUSTOMMOB_spawn_egg",
    "count": 1
  }
}

Replace Misc by your mod group name. On your workspace, click the blue icon on the top right, it should be called "Workspace Settings", On it copy the Mod ID Namespace, paste it there instead of Misc.

Mate... I told you, ONLY EDIT THE LINE FROM ITEM,.....
Look at what I've said at first, see?
the "group" and "item from key" is automatically set by mcreator to the ones you set on step 2, the thing you just need to edit is on this is the result - items.

The MISC on group tag is the one from the creative tab, if you didnt add a creative tab, of course it will not work.....

The reason WHY i've said "group": "YOURMODGROUPNAMEHERE", is because I thought you already have a creative tab of your own. but instead you use Misc minecraft creative tab....

JUST EDIT THE RESULT. DONT DO ANYTHINS STUPID ON THE GROUP TOP TAG.

"result": { "item": "manacraft:Abominable_snowman_spawn_egg", "count": 1 }

This is already correct if your mod id nameplate is manacraft and your spawn egg name is Abominable snowman.

hey uh how do you change the last line to something custom mine stays as "minecraft:pig_spawn_egg" and i cant change it

please help me

my code looks like this and I CANT change it:
 

{
  "group": "mog",
  "type": "minecraft:crafting_shaped",
  "pattern": [
    "012",
    "345",
    "678"
  ],
  "key": {
    "0": {
      "item": "minecraft:redstone_block"
    },
    "1": {
      "item": "minecraft:redstone_block"
    },
    "2": {
      "item": "minecraft:redstone_block"
    },
    "3": {
      "item": "minecraft:glass_pane"
    },
    "4": {
      "item": "minecraft:white_stained_glass_pane"
    },
    "5": {
      "item": "minecraft:redstone_block"
    },
    "6": {
      "item": "minecraft:redstone_block"
    },
    "7": {
      "item": "minecraft:redstone_block"
    },
    "8": {
      "item": "minecraft:redstone_block"
    }
  },
  "result": {
    "item": "minecraft:pig_spawn_egg",
    "count": 1
  }
}

oh wait nvm