WIP Adding a monster without replacing

I have created a creature and I can spawn it in and it spawns in the world naturally. The issue is that I don't know how to have it without replacing another monster. I want to add multiple monsters to the game, but the way I added this one is by editing a monsters file and using a json file I told it to use my files instead of the games ones. It works fine, but I want to add monsters without replacing the already existing ones! Any help is appreciated.

 

I just realised this is in the wrong place, please don't be mad at me, I'm very new. Google says a Moderator needs to delete it and I can't find any way of deleting it myself. Again, very sorry!