How are "rare, non static" mobs done

[ShivanAngel]

I read in a post that some of the rare mobs that didnt have a set placeholder (quillmane, grizzlebark, etc) have a new way of spawning in P99...

How are these mobs done now, did they just make a random mob or two its placeholder and thats how you spawn it now.

If this is in the wrong forum or information I shouldnt know let me know hehe.

Mainly want to know because I want to go after pyzjin for a GBS and if she spawns different now thats good info.