Those of you who play may have seen from time to time a monster deal damage to another one by accident or even kill them (back before a certain FSC update it was actually a viable strategy to take advantage of this).
http://doom.wikia.com/wiki/Monster_infighting
What I would like to propose is a sort of monster infighting where monsters can actually target others that aren't in their group.
Group 1: Beast and Slime
Group 2: Gremlin and Construct
Group 3: Fiend and Undead
Unaligned group: Healer monsters, certain mission monster combos, minis, event monsters, bosses
Monsters in different groups can deal damage to each other (type damage included) and there may be infighting amongst them if the player is out of detection range or if they deal enough damage. Monsters in the unaligned group cannot deal damage to other monsters, and healers cannot be targeted but can be hit.
Certain missions that combine monsters of different families will not have this infighting but those that don't can have infighting.
Example: Rotting Metropolis, Ghost in the Machine, Heart of Ice, etc.
Note: this damage from infighting is comparatively weak to the damage you can deal to the monsters and vice versa
I would love this kind of game play atmosphere in sk. I remember when 2 giant linchens use to target each other in sk, but now they do not act the behave the same way probably cause of an update. Anyway, this kind of infighting behavior would show that monsters can actually relate to each other abd have a relation that is not always friendly. It would show that these groups of monsters can actually have tension between each other. It would be a great game play aspect to have where we can see monsters do actions that are rary seen. And we can balance this by making the damage they do to each other relatively weak similar to a catalyzer regular bullet or more.
Also, i think we should instead make it so that families fight each other, and not just some groups. Also, make it so that certain monsters in a family can also fight each other like a trojan fighting a greaver. This way we can still see this kind of behavior in levels that are family theme such as an all beast family level. Or an all fiend family level.
To push this even further, we can even make it so that mini-boss monsters would command weaker monsters around ot to attack one monsters that is out of line or rebelling. This way we can assume there is some kind of cammand structure relationship in these monster families/interactions.