I'm trying to put a spawn egg for a custom entity I made into a custom creative tab. I register the entities with this method, which creates a spawn egg for them as well:
public static void registerEntity(String name, Class<? extends Entity> entity, int id, int range, int color1, int color2)
EntityRegistry.registerModEntity(new ResourceLocation(Reference.MOD_ID + ":" + name), entity, name, id, Main.instance, range, 1, true, color1, color2);
Mod for 1.12.2. Adding onto Minecraft while staying close to vanilla.