So you're running a campaign, DM introduces an NPC.   He's all friendly and following the party and helping out a lot.  Surprise, the NPC turns on the party and has his/her own objective.   Party is caught flat-footed, "How could this happen, he's been a loyal and trustworthy friend?"

Fast forward past the betrayal, another NPC is all "I'm a great elven prince and have the same goal as you.   Lemme help out!"

Surprise, the NPC elf also betrays the party!    Huge plot development, NPC we trusted betrays us.

Fast forward to the next town, an NPC want's to help out the party.

Me, "I shoot the new NPC.  Rolling initiative now."

DM, "What?  That's totally uncalled for.   Why in the world would you want to shoot an NPC that's trying to help the party?"

Me, "So you're saying I get a surprise round?!"

Isn't this just due to the DM being lazy and constantly repeating the same surprise of "NPC betrayal"?

As a DM I would think this would be used very rarely to ensure it holds the weight it's supposed to and introduce NPCs who are exactly what they seem or may have ulterior motives but nothing that involves actual betrayal. This way NPCs have variety and a longer lasting impression and can be re-used in future developing friendship and alliance over the course of the campaign.

I agree.  My DM introduces NPC's who really do help us as well as NPC's who betray us.  That's fun.  Having every single NPC betray the party get's boring.

I am currently using the NPC betrayal plot. It's been extremely difficult trying to keep ahead of the players who, because they know me, anticipate that not everything is as it seems. Now, I have never done this plot with this group, however I have used other situations that turned out to be different than what they seemed. What we have in the first post is both lazy DMing and an over used plot device. The betrayal plot arc should have both story and emotional resonance, something that carries a weight that isn't soon forgotten but is only tied to that political event and that person/group. Creating a sense of caution when dealing with unfamiliar situations is all well and good, but when the party immediately distrusts anything that is not part of their group, you've made a serious mistake.

The way the OP handled the situation, whether hypothetical or legitimate, is entertaining to imagine but damaging to the table. After that session, I would have to suggest that the player(s) address their frustration with the DM. As hard as it is to admit, being a DM myself, we are not infallible behind the screen, we get caught up in the moment, we forget what we're doing, and we tend to drop into predictable patterns when we're out of ideas. Have a talk with the DM and let him/her know that you/the group is getting burnt out on that plot device and would like to see it used less often. With any luck the game will change up, you'll make a friend or two out of the NPCs and your party won't be forced to become a bunch of genocidal murder hobos.

As someone who classically calls himself a "Shadowrun Player", and builds his D&D characters like they are Shadowrun characters.

"Mr. Johnson" is probably always going to betray you. It's the trope.

After having a couple of NPCs come along, appear helpful, join the party and then turn around and betray the party ... I can easily see the party refusing to work with any NPCs unless they can prove in some way that they are trustworthy and reliable. I wouldn't necessarily shoot the NPCs that come up and offer their aid (though it is tempting and I could see this role played by certain characters who might just decide that folks who act nice out of the blue can't be trusted) but the party is very likely to be leery of any NPCs who come bearing gifts.

From a DM perspective, it would appear to be a case of an overused plot device. If the DM teaches the party that NPCs can't be trusted then why would he expect any other reaction than distrust or animosity towards other NPCs? The party would have to be somewhat unintelligent to keep falling for the same situation. Part of the reason the NPCs were accepted into the party in the first place is due to an implicit trust in the DM wanting to run an fun story line. If the betrayal isn't fun for the players in the end then the DM is kind of missing the point :)

Finally, as for attacking random strangers when they try to be nice to the party ... the party may find out that the random NPC is more powerful than they look ... or perhaps local constables intervene and lock up the party members involved in the attack .. or any number of possible consequences.

Quote from FullMetalBunny >>

As someone who classically calls himself a "Shadowrun Player", and builds his D&D characters like they are Shadowrun characters.

"Mr. Johnson" is probably always going to betray you. It's the trope.

Quote from RenFaireMan >>

 

Me, "I shoot the new NPC.  Rolling initiative now."

DM, "What?  That's totally uncalled for.   Why in the world would you want to shoot an NPC that's trying to help the party?"

Me, "So you're saying I get a surprise round?!"

I was running Princes of the Apocalypse and told my PCs that they found a note on the corpses of people who tried to kill them that was signed with the initials T.M.  They decided to trust Thrul Merosska for some reason.  Bad idea . . .