I guess along with adding that there are more peaceful monsters than ever before (I stepped on a teleporter yesterday and all 3 monsters in the room were peaceful) I am seeing more monsters run away in fear. What triggers this?
The usual way is: kill the leader of a group of minions in their presence and the ones that are left will scatter. There's probably a skill effect for it as well, but I haven't encountered it in any of my builds to date. It may just be RNG screw, but since CotW popped I've been seeing a lot more non-Inconsequentia "this monster is the leader of..." spawns without the Named Monster Glow Of Doom, then had to chase the others down because their leader got kersplatted first.
I think the "scatter when leader is killed" is actually a great addition. It should probably be accompanied by some flavor tet "Run away!", but it creates, potentially, new tactics. Where your focus is on killing a single character to get out of a bind rather than just looking for a bottleneck.