Looking at the artwork of a wizard fighting a priestess, I've noticed a group of soldiers running from behind the priestess. That made me thinking about having some kind of creatures with a "horde" (or swarm, pack, whatever will be more suitable) trait. Those creatures should be most probably a group of weak ones, like a group of conscripts, a flock of birds, a swarm of lesser imps or anything in similar vein. That way it will keep their power in line with other creatures, because summoning a squad of elite knights of Westmarch would look stupid with a mere six attack dice (unlike a group of conscripts, who can possibly pull off six attack dice worth of damage) and also I don't intend to turn the game into Commander Wars.
I know that this alone wouldn't warrant a creation of a new trait, so I thought that they should have some kind of extra effect. Like either having enchantments (or possibly all spells targeting them increased cost to represent the difficulty of casting something on a group of creatures, instead on just one. Maybe with the exception of spells within the same schools as the creatures (as some kind of close affinity or something), maybe even requiring the mage to be trained in that school as well.
Extra options include enchantments from mind school being immune to the increased cost (representing the fact that a mob can be manipulated easier than a single person), or having the group's attack gradually weaken as its hitpoints decrease (for example 4 attack dice and 12 health, every 3 health lost will weaken the attack by one die and increasing their health will just add extra health before the attack starts to weaken).
I know that this may not be worth much (if anything), but someone may be able to salvage something out of this mess.