So the first thing I would do upon getting that background is figure out what level the uncle is. A level 5 adventurer uncle will have far less monsters encountered and learned about than a level 15 adventurer uncle. Then I would look at the area of the world the uncle adventured in and what monsters would be commonly encountered up to his level. For those monsters, yes the PC would get a check and I would treat it similar to having a knowledge skill. The DC would be the same as someone who didn't have the background, but had the appropriate skill.
Seems like potentially a lot of effort to avoid an otherwise simple solution. I think that, as with many examples, you're assuming that the player continually does this kind of thing. He's constantly introducing new uncles that have various areas of expertise and who have imparted their knowledge on the character. But that's not what I'm talking about. I'm talking about one instance, and it was an instance related to the players being uninterested in the content of play, so they help move things along.
That specific example aside, I don't have a problem if the dice are used to determine such things. Maybe the uncle is introduced to the fiction as a result of a successful dice roll. I think that's the kind of emergent play that many are advocating.
I ask my players for a written background so that I have an idea about their PCs. It's not all encompassing, but it gives a pretty good general idea of what they might know or not know. They can add in more details later, but only with respect to something they've put into their background. For example, they can add a limp to their uncle received by a raging owlbear later on, so long as the adventurer uncle was in the original background. They can't just keep adding in new uncles to suit their desires.
Why not have them create that background as you play? Why write anything down ahead of time?
I genuinely mean that. I am not saying that writing a background is bad in and of itself, but rather that it has pros and cons. One of the cons seems to be it locks things in place, but the brief nature of such a background means that what's locked in place is limited.
It seems arbitrary to me to hold the players to that kind of limited detail. Again, nothing wrong with writing it down, but I think allowing for additions to their background is likely a good idea.
The players know about the HPs and other resources, but the character does not. The character would be aware that he is tiring and getting bruised up, slowing him down and/or making him more sloppy, which is more likely to get him killed, but he won't know that he dropped from 30 hit points to 10. The player is the only one to know about something like second wind. A character isn't going to be able to just trigger a second wind at will. Second winds come when they come in the game world, but outside of that the player is choosing. Since metagaming is having the character act on player knowledge about something the character wouldn't know about, none of that is metagaming.
The character would, whether at full HP or 1 HP, expect a flail strike to the head by a gnoll to be a lethal blow. However, when the fighter has full HP, he will be less concerned about any individual attack. Hence, he is acting on the game mechanics, or out of fiction knowledge.
Again, I don't have a problem with this. I just think it demonstrates that metagaming is present in every game, and is actually often very beneficial to play.
Bringing out of character knowledge into the game is where metagaming happens.
Sure. Whether that's a bad thing or not, and whether the DM can block it, is what we're talking about. Again, I know you're coming at this from a D&D perspective, but to insist that metagaming is always cheating is where I disagree.
In my game players can pick any common background. If they want a chance for something better like nobility, they can roll for it and if they get lucky, they are a noble or come from a family of wealthy merchants, with all the advantages that come with that. However, if they roll, they can also end up a street urchin, which comes with less money than normal. It's up to them if they want to chance it.
Okay. I personally find that such backgrounds are not "better". They may offer an advantage such as more starting money, or maybe an extra skill or language or something similar. But they also often come with related drawbacks....familial obligations, established enemies, expectations of behavior, and so on.
No they don't. The first half of hit point loss never even touches the PC at all. A 100 hit point fighter would have to be at 50 hit points before he takes even a scratch or bruise. Then it takes hitting 0 before any major wound happens, and that's all it takes for a high level fighter to potentially die. One hit. The other "hits" aren't really hits. They're close calls that the character isn't aware of as hits.
Well, this is your very specific take on HP. There are many ways to narrate HP and what they mean (and I don't want to add that topic to this debate as well), but this doesn't change the fact that the character with full HP will tend to act more decisively because he knows he's at less risk of dying.
Because one is all about unfair advantages and the other is not. If the player waits until he is right in front of a hydra to tell me that his uncle was a hydra hunter, that's really hinky. Setting it up in advance, though, doesn't guarantee the player that it will ever be useful as the PC might not encounter a hydra. It's just a background piece that may or may not be useful. Personally, I like bringing bits of PC backgrounds into the game. I've found it makes the players happy when it happens and it's fun to surprise them with something like that.
I wouldn't say it's an unfair advantage, especially since the players already have the knowledge. Rather, it's a way of reconciling that player/character knowledge discrepancy.
I get the distinction you're making, but I don't think it's an unfair advantage so much as
having to commit to a background detail at the time of character creation knowing it may never be relevant is more of an unfair disadvantage. Isn't it cooler to have characters whose backgrounds matter? Isn't that better for play?
This is the kind of relevance that many are pointing toward. Sure, the DM can take a background element and incorporate it into the story...I do that all the time. But letting the player introduce it as it comes up ensures that it happens, and that it happens in a way the player would like to see. And it really shouldn't be a hindrance to the DM in any way....so I really don't see the issue.