offensive spells work np
but the fights arent interesting if everything just cast a green or black fireball 
what make fights interesting is the interaction between the same faction, if you have played wow you understand what i mean
thats why i need monsters to do some stuff to each other to make more complex fights
anyway yes i thought a bit and few things can be done with passives
for example thinking about wolf mom and children i though a way to make mom enrage if children are dead but its quite complicated
i make a hidden stat on children buffing every other friend stat "is alive"
then i make passive aura for mom buffing stats if "is alive" is 0
eventually i could add a bonus to some active skills like a bite or something
still its not enough, when everything is passive its less fun imo