I use some rough "math" here, so take it with a grain of salt as this is very anecdotal from my personal experiences.

Fighting is pretty rough and brutal in BoL, and so is healing after, so I like to keep that in mind when there are combats. Usually this is my math set-up:

2 Rabble = 1 Hero

So, let's say a group of 4 heroes and I want to challenge them a bit. Throw in a "standard" NPC and six rabble. This has worked well for me in the past, but sometimes when the dice are not in the players' favor, this can hurt a lot more.

Or, if you want to embrace some pulpiness, which is fitting for the syster after all, have four rabble assault the four heroes with extra rabble to jump in as it feels right. Kind of like kung-fu flicks where the mooks all try and take on the hero one-on-one while the others watch on, waiting to jump in. This also works well in my experience.

Great point, MarCazm. I usually run with lots smaller groups, so the dynamic is definitely different for me. Now I want to swarm a larger group with rabble!

MarCazm for the win - swarm 'em every time! Then they get to show you just how good they are.

My wife's character took out eight assassins with one legendary success - she'd always played her PC like a badass, but that proved it. Made the game for her.

I sent ten rabble against four beginning characters and they handled them fairly easily (but they did burn 5 Hero points between them). They'll probably regret that a bit later in the adventure ...

In the mythic Simon had said just one attack roll with +1 to hit per member of the rabble mob (limited by how many could rationally be engaged with the hero.) Instead of damage being d3 (standard for rabble), it would now do 2d6/Low damage. If not using mythic then I guess you could use the same method for attack and add 1 to damage.