As if the nuclear apocalypse, having my wife murdered and my son stolen wasn't bad enough, Fallout 4's Mongrel dogs are about to get tougher. I hate Fallout 4's Mongrel dogs at the best of times, thus the idea of them becoming more socially aware in battle makes me feel a little queasy. 

Greslin's Pack Attack Fallout 4 mod is responsible for this, as it attaches a script to all Mongrel dogs that continually evaluates the canine's "current immediate social environment and threat situation". In turn, if a dog senses other dogs nearby, it'll become more aggressive in the knowledge its backup isn't far off. If it realises it's on the back foot in any given fight—ie, if it can't find its companions, or has taken a lot of damage—it's more likely to turn tail and run. 

"This essentially means that Mongrel dogs, especially when they hit in packs, are now a lot less predictable," says Greslin. "And more dangerous." Great. 

Here's Greslin with the skinny:

In the vanilla game, an Actor (you, me, dogs, robots, etc.) has an Aggression stat (how likely it is to attack), a Confidence stat (cowardly/brave/foolhardy), and a general Combat Style (which specifies combat behavior in more detail).  Normally these stats are hardwired into Actors, including dogs.  If an Actor is a coward, they're usually - but not always - a coward forever. Thing is, I've never been satisfied with how Fallout 4 handled Mongrel Dogs.  I like dogs, and I've always felt that Mongrels needed a lot more social awareness and cohesion than simply being a go-kill-em melee torpedo on four legs.  And, it turns out, the above stats can all be changed on the fly.

When a Mongrel is loaded into the game, it will immediately do a threat assessment (am I being attacked?  is there an enemy nearby?) and an immediate area scan for other Mongrels.  If it finds other dogs, it will act more confidently and aggressively as a pack attacker.  On the other hand, if it realizes that it's the last dog standing, or it's been seriously hurt, it's a lot more likely to tuck tail and run.  Combat styles also change appropriately.

More information on Pack Attack, including installation instructions, can be found via the mod's Nexus Mods page.