Just thinking outloud...I believe you can have NPCs spawn either by spawners or by settings in the playfield.yaml for the biome or planet. I'd be interested in knowing the differences between these two methods.
Using the Playfield as the spawner eliminates the need for the a visible item that can be destroyed, and creates a replacement NPC when its killed, then you would have to look at timers and whatnot.
Same with every creature that has a spawner as Far as i know. I have not tried them all, but what I have tried fails every time.
I posted one that I made here http://empyriononline.com/threads/custom-playfields-by-vexray.6864/page-4#post-68519 I found it to be fairly easy with a sniper rifle...
I'm collecting information, guides, etc., to put everything related to EGS in one central place - Empyrion.org. (It's new, I haven't even made an introductory post for it anywhere). What would you like to see there? If all of the information for planet customization is here on the forums, all I need to do is track it down. If you already know where to look for it, kindly point me in the right direction!
There is already an empyrion wiki page .... do we need another though? The idea is to keep all the information in one place, so making more websites actually does the opposite.
I made a video tutorial for this on my YouTube channel if you want to check it out. I'm not sure if it is going to answer all of your questions, but it does go over most of everything I had learned about custom playfields up until then. I've learned more since then and might make a newer and better organized video at some point, but for now this might help.
