As discussed here:viewtopic.php?f=3&t=31059&p=588239#p588239
and in another relatively recent thread (not by me) that I can't find ATM.
It would be useful to be able to have a flag (+FORCEINFIGHTING) that forces a particular enemy to always display the normal Doom infighting behaviour (and, I suppose, a way to have an individual enemy type to always act as if no infighting was set (+FORCENOINFIGHTING)).
At present, the game can be set so that all enemies will never infight or that all enemies will infight if damaged by another enemy. Sometimes, however, it would be useful to have an actor that bucks this particular trend and does the opposite to what the over all game setting says. I know that things can be set up using "species" relationships but that can involve a lot of work (possibly editing all the actors in the game) if all that is needed is just to have one actor type that does the opposite to what everyone else is doing.