I've observed that when a MOB's factions are defined directly in World Builder (WB), which overrides the setting in it's proto, things get a little problematic. Whenever a MOB is given more than one faction in World Builder WB, it seems to only recognizes the first one. I was told that you need to put a "0" after each faction listed in WB when you create a MOB, but I'm starting to question the need for that "0", as it seems to be the root of the problem. (As most people know, if am NPC is attacked and it has at least one matching faction number with another NPC standing nearby, both NPCs will join combat if either one of them is attacked. So, if you attack an NPC with factions "9 12", a nearby NPC with factions "9 11" will enter combat, since they both share a "9". An NPC with factions "1 14 22" will ignore the fray, unless attacked directly.) Some examples to clarify my observations: Example 1: If two MOBs have their factions set as follows, everything works fine. Nothing unusual. Code: MOB 1 MOB 2 ----- ----- 9 9 0 0 Example 2: If two MOBS have their factions set as follows, everything works fine. Nothing unusual. Code: MOB 1 MOB 2 ----- ----- 9 9 0 0 11 12 0 0 ** THE PROBLEMS START HERE ** Example 3: If two MOBS have their factions set as follows: Code: MOB 1 MOB 2 ----- ----- 11 12 0 0 9 9 0 0 The second faction in each MOB (9) seems to be ignored. When the first MOB is attacked, the second MOB does not join in. And if the second MOB is also attacked, he joins combat, but doesn't get along with the first MOB. He'll take attacks of Opportunity on the first MOB, etc. It behaves as if the second faction in the list (9) is not even recognized, and it's just one MOB with faction 11, and the other with faction 12. (Note: This example has the same problem if the factions are changed to "1 0 9 0" and "2 0 9 0", so the problem is not that they are out of order numerically.) ** THIS NEXT EXAMPLE WORKS JUST FINE , CONTRARY TO WHAT I'VE BEEN TOLD ** Example 4: If I break the rule about adding that "0" spacer, everything works. The matching faction of 9 is recognized and the two MOBs fight together: Code: MOB 1 MOB 2 ----- ----- 11 12 9 9 So, what's with that "0"? Is it really needed? It seems to void out any other faction that comes after it. Maybe this was never noticed because "9" is always listed first in most cases where a MOB has multiple factions.