At gunpoint

[SpiderBrigade]

Yeah, this is one of those things that will come up, because it makes a really great dramatic scene. Or at least it would, if the PCs didn't just say "hah, okay, shoot me with that crossbow! I have 150 HP!

Letting it count as a Coup de Grace would probably be enough, really. At least, it would if the NPC is in fact a rogue, with sneak attack dice. With a crossbow, the save will be 10+2d8+howevermany d6. Vs death. Sure, the NPC might roll nothing but ones and the save'll only be DC 15...but he might also NOT. That puts the threat in the range of things the PCs can't comfortably ignore.

Edit: multisimued, of course. @ClementX: that seems like a lot of "ifs," possibly too many for this to be a tactic that would ever be used. I think the idea is that, realistically, if the bad guy sneaks up behind you and suddenly you have a gun/crossbow to your head, he shouldn't have to have 8 levels in rogue and a specialized feat to be seriously threatening to you.

I'd say the best choice is to relegate this tactic to "used-vs-NPCs-only." Allowing the heroes to be held hostage takes some control out of their hands and would be frustrating, because they are almost inevitably going to think metagame and "heroically" ignore the danger.

On the other hand, if the evil NPC puts a sword to the young prince's throat (level 1 aristocrat) he COULD reliably kill him. So the PCs have to pay attention, and since the prince is under your control, he won't be stupidly heroic.