Guys i have a question, its the natural spawns
So... spawn weight, higher means it spawns more of the npc or less?
Cause with other mods, sometimes lower means higher chance, and then there's times when you set it to higher and it becomes more rare
I just want to know which way it works here on custom npcs, if i set it low enough does that mean the npcs spawn more commonly?
Neither. Spawn weight is the likelihood that if something were to spawn, it'd be that NPC. So basically it first decides if it's spawning anything (Usually this is determined by vanilla MC or any spawner mod you may have installed.) If it is it consults spawn weights - The higher the weight the more likely that the thing spawning will be that.
So if you only have one NPC it doesn't matter what it's spawn weight is - If it's spawning something it will always be that NPC because it's the only one. If you have 2 NPCs, both with the same spawn weight, it's a 50/50 chance which you'll get. If one has a spawn weight of 1 and the other has one of 2, then the one with the spawn weight of 2 is twice as likely to spawn than the other NPC.
But still, spawn weight doesn't control whether something will spawn or not. That's determined before spawn weight is factored in. So if you want something to be super rare, give it a spawn weight of 1 and then another NPC with a spawn weight of 100. It won't make NPCs rare as a whole, but the vast majority of those that spawn will be the one with the weight of 100.
BTW, most mods use weights in this same way. Many don't have options to configure the amount of spawning happening, only the weights which affect what will spawn. If you want to control the amount of spawns you usually need a spawn control mod. I'm not sure if Custom NPCs has an option for spawn chance, but most likely not.