Was looking around for this on 6.x but to no avail so after testing some I figured I’d post my results in case anyone was wondering or wanted to make the optimal feign death npc. Few have similar flags to these but they usually have some huge unit2 flag which isn’t all necessary for a basic feign death npc. Heres what I used:
Unit_flags = 537002754 (Incorporates unattackable, pacified, immune to pc/npc combat, and feign. The creature remains targetable.
Unit2_flags = 2049
Dynamicflags = 64 (this is the most important)
Type_flags = 0
Flags_extra = 0 (2 if for some reason there is still a problem with aggro.)
Been using this combination to correct several NPCs that didn’t have the proper ones set and they have tested fine alone and with other creatures around attacking.