Since this mod is now dead (R.I.P) would you please talk about how the Npplayers worked? Like how the code and scripts for them worked, so that one day someone might come along and build upon it.
For the npplayers to work, I had to overwrite a serie of things on the Player character AI.
Not only I had to make changes so in the place where the player can take an action (controls), it checks if the player is a npplayer, then if is, directs the script to a place where the npplayer AI tries to make use of the player controls just to do the movement and stuff from the character, and so entered part of the ai and stuff, aswell, but I also had to individualize their aim, since the player aiming on Terraria is bound to the mouse position.
Another thing I had to do, was to do scripts to check if the player is a npplayer too, otherwise, the scripts would check if is the main player and scripts like inflicting damage and some projectile AIs would either not work correctly, or break.
I really believe that making npplayers on tModLoader isn't possible unless the devs of it do extensive changes to the Player AI, and do variables to either check or bypass some conditions on npcs and projectiles, because even if you manage to make the npplayers be able to spawn or move through the world, they possibly would end up immortal.
Ps:. The mod isn't really dead, I'm just being lazy to do some work on it, I've even released a spoiler somewhere of recent stuff I did on it, beside I think the mod would be too outdated for now adays Terraria'ing. Just check my profile for them.