How does this guy work exactly? I saw him by chance while exploring, but got distracted by grave robbers mobs and then he disappeared. I've checked all of these 3 locations to see if I could find him again, but no success, even when changing channels.

Edit: Found him on the spot in Kolsh Valley totally by chance while changing channels. His HP is not shown for some reason and I got super desperate to kill him fast so I couldn't take a screenshot, my bad. But if I had to guess, it seems he has some sort o long respawn timer and maybe can only spawn one time at one of these 3 spots.

Do not attack the ghost follow it around. The hearts above its head appear to be a gesture of trust. On completion it will automatically add to the adventure book.

Sharing my experience with this mob for those who saw it but disappeared from you. The 3 locations are where it spawns, if you don't see it in those locations try changing channels. It drops a rapport Rethramis Holy Water when killed.