So how does each deal with the killing of an NPC who would give a plot-important quest? Or is the main quest given right from the start?

You can find ways to deal with it if you realy want to. You can make quests failsafe by leaving a note on the body, or leaving quest reward reachable after death of the NPC. Or your npc may not die in a plausible way, like teleporting to escape, a cutscene that saves him from players grip.

The main question is what do you gain from killable NPC's and how commited are you to the concept. Because it will haunt you all the way through the development as you implement guidelines to support this idea. It may also cause problems after release when you forget something and the players get stuck because of their ill decision.

I am personally in favor of attackable NPC's. However it is not without negatives. I have found the idea of killing NPC's only meaningful when the game permits player to impact the world. Otherwise disadventages quickly pile up against advantages, on a developer's point of view of course.

From a player's perspective (as opposed to a developer's), is there anything that can be gained from an unkillable NPC? Or should all NPCs be attackable? Of course, some, like your mentor at the beginning of the game, will be too strong to kill.

The only reason I can think of to disable attacking NPCs is to prevent accidental attacks, which is why some games have an option to turn Friendly Fire off. But anything else?

In single-player RPGs the bonus for the player is that they don't accidentally stop themselves from finishing the game/having to redoing content.

In multiplayer RPGs it has the benefit of limiting griefing. Another player can't stop you from handing in a quest by killing the Q giver.

Personally I prefer having killable NPCs, it makes the whole thing more believable and less "gamey". Although in single player games it goes hand in hand with a decent autosave system.

In Fallout 3, I encountered issues with unkillable NPCs. I decided to go bad karma for a while (okay, actually a quest glitched, I got annoyed, and decided to kill everybody in Rivet City by littering the place with mines and opening fire). One character was unkillable for quest reasons, an optional quest that I didn't want to take (or perhaps a mandatory quest I'd already done). He pretty much turned into the Terminator. It was slightly scary. What good is a questgiver that wants you dead and can't be killed?

For me the unkillability breaks immersion. Some warning would be nice, e.g. they give some dying breath message or leave behind a scroll, etc. Even what SOTL said about Elder Scrolls. Although that could go horribly wrong if your cousin plays for 5 minutes, kills an essential NPC, then doesn't tell you about the message. ;)

The first reason s the one you mentioned: you don't want to accidentally shoot a fireball in the king's court, kill the entire royal family, and completely derail the story.

The second is that it may not fit the story at all. If you're a Pokemon Trainer, the you are a kid obsessed with these fantastical creatures, not a psychopath that will kill other kids and shopkeepers to steal their Pokemon and special items. If you're a paladin, then no, you can't kill that widow that asked you to find her only son, no matter how much her sobbing and pleading irritate you.

The second is that it may not fit the story at all. If you're a Pokemon Trainer, the you are a kid obsessed with these fantastical creatures, not a psychopath that will kill other kids and shopkeepers to steal their Pokemon and special items. If you're a paladin, then no, you can't kill that widow that asked you to find her only son, no matter how much her sobbing and pleading irritate you.

Also, players are don't always good roleplayers or know what they want to experience, how they want to experience. Some times it's okay to limit them to deliver better experience. As for breaking the immersion, maybe you should work something out for a way to keep key NPC's alive without butchering believability.

Yeah I think this is kind of like "friendly fire" being always turned off in multiplayer shooters. Too many people were massive dicks with the feature to make it a good game design decision, even if it increases realism or makes the game more interesting.

Yeah I think this is kind of like "friendly fire" being always turned off in multiplayer shooters. Too many people were massive dicks with the feature to make it a good game design decision, even if it increases realism or makes the game more interesting.

But that design decision depends on your community. There are games that do friendly fire very well, because it works with the community that plays the game. (It's not always better to make friendly fire off, even if most of the time it is the best choice. There are no blanket design rules )

I'm surprised no one has mentioned Deus Ex. It was another game that would allow you to kill almost anyone (other than key plot providers).

One time I was playing, and I walked into the 'ton hotel with my gun out - a bad move. Jock (the helicopter pilot who shuttles you around for half the game) pulled his gun out and started a massive fight that I couldn't win - he was invincible. It still made for an entertaining few minutes though, until I died and had to re-load.

To me, it comes down to what the designer wants. If you can think if alternate ways around things despite there being dead NPCs, go for it. In my mind it would help the immersion a bit (unlike the invincible helicopter pilot).

I say if you do decide to make a game with killable NPCs DON'T make them plot-detail essential (use artificial means of plot advancement like the "angel" in Borderlands or whatever works for the game; OF COURSE this only applies if you don't want to make tons of extra branching events for world/social simulation) and DON'T just make the standard "kill NPC for XP and items at the cost of reputation/bail" design choice. I say that second part only to persuade you to be a little more creative.

Example: You cannot kill an NPC directly like you would an enemy, but you could pick them up and throw them at enemies like weapons or use them as bait in traps (plus a lot more I haven't thought of). In this way I think killable NPCs become more of a gameplay mechanic (like a 'resource') rather than just fluff for realism with a reward.

These are just my opinions. Use of them what you wish.