I have decent coding experience but just started making Minecraft plugins. Anyways, there's an item Reaper Scythe that I want to make. It makes it so that when you kill a mob it becomes like your pet, in the way that it attacks anything that you attack, or anything that attacks you. I really don't know where to start. Any help would be greatly appreciated.
You need to make custom mobs with custom pathfinding, just copy the wolf's pathfinding and behavior and make your mob do the same. There is a lot of guides on the internet about how to do this exactly, just google it.