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Shadowknight12
2012-03-17, 01:43 PM
Is there a dish that gives food poisoning sufficient to make you violently ill, but likely will not kill you, unless prepared with about the same care as fugu? That'd be closer.

Not preparation, but if you're not an expert at picking what "wild mushrooms" you're going to be adding to your meal, then roll a d100 and consult the following table:

{table]Roll|Effect
1-10|Nothing happens.
11-30|Mild discomfort occurs 10d4 minutes after the meal.
31-50|Heavy discomfort occurs 10d4 minutes after the meal.
51-70|As the previous one, plus make a Fort save, DC 18, or take 1d6 Con damage.
71-90|As the previous one, plus make another Fort save, same DC and Con damage, every 1d4 hours or until you succeed.
91-100|Make a Fort save vs. death, DC 19.[/table]

JadedDM
2012-03-17, 02:15 PM
Yet people pay a lot of money to eat Fugu.

And as I said, its not a good analogy. The risk/reward balance is heavily skewed. A DMPC does not carry a risk of death, unless you are playing with somebody who is homicidal, but that would be a seperate problem. How about a souffle? Its hard to do, and many people will fail. And honestly, its just a light, fluffy desert. Is it worth the risk of a failed desert?

You're the same guy who keeps comparing dislike of DMPCs to racism, right? I think nitpicking the Fugu analogy is a little hypocritical there.

Besides that, I think you are missing the point. Look at the title of this thread. It's not, "DMPCs--are they really so bad?" but "DMPCs--good for the game." The point we're trying to get across to you is that when used poorly, DMPCs ruin games. And when used well--they don't hurt anything but don't add anything of value, either.

So I suppose the perfect food analogy would be a meal that makes everyone sick if done poorly (and is so difficult to pull off, most people do it poorly) but when done well, is completely tasteless and doesn't add anything to the overall meal.

Jay R
2012-03-17, 02:49 PM
So you would never play a module/adventure path with someone who has already played/run it before, because the player has an "unfair advantage"?

Well, actually, it hasn't come up. I haven't played in a packaged module/adventure this century. The DMs I play with have too many original ideas themselves.

The last adventures I've seen used were in a game of Flashing Blades I was running in the nineties. I made sure nobody else had seen the adventures. If anyone in the party had seen them before, I would have either not used them, or made some crucial changes to them, so those players can have the surprises a game is supposed to have.

Why wouldn't I want them to have all the fun the game offers?

pres_man
2012-03-17, 03:00 PM
I think having a constant character that the DM can use to interact with the party in game and in character is of some benefit in a lot of situations. If a different random townsfolk in each town that the party comes to know exactly what is going on and can remind them why they are there, that really breaks the immersion for some people.

"Yeah I know you've never seen me before, but I'm here to remind you that you came to this town to seek out that amulet in the ancient ruins. I know all about you and your deeds, because I am just another random NPC used by the DM to interact with you."

Yeah, I know the response, "But that is railroading!" Or maybe it is not. Maybe the players have taken a break for a time and don't quite remember what their characters were up to. Maybe its been 3-4 weeks due to Finals, Christmas, New Year, and whatever, since the whole group got together.

And yes, you could rehash it all out of game, but some folks actually like to, you know, roleplay, as crazy as that is, I know.

Which brings up a thought. In the two groups I game with, the one group that uses the pronouns "I and me" most often is also the one that doesn't roleplay very much. They don't have characters they have proxies. Their characters are as significant as playing the boot in Monopoly. The other group that actually roleplays their characters as individual characters separate from the person playing it are more likely to say "Darken does ..." They still say "I" and "me" as well but the other group uses those pronouns exclusively where the roleplaying group varies from time to time.

Shadowknight12
2012-03-17, 03:03 PM
Why wouldn't I want them to have all the fun the game offers?

I know it's hard to realise, particularly since you seem to have 20+ years in the roleplaying business, but not everyone derives fun from the same things you and your group do. I make a habit of confabulating with players/DMs to make sure that we're on the same page in some things, and I am completely sure that if you heard our conversations, you'd say we're defeating the purpose of the game by destroying the element of surprise and discovery.

So really, I know it's hard and probably even counter-intuitive, but do try to keep in mind that not everyone plays D&D like your group, or for the same reasons. :smallsmile:

Sucrose
2012-03-17, 03:10 PM
I think having a constant character that the DM can use to interact with the party in game and in character is of some benefit in a lot of situations. If a different random townsfolk in each town that the party comes to know exactly what is going on and can remind them why they are there, that really breaks the immersion for some people.

"Yeah I know you've never seen me before, but I'm here to remind you that you came to this town to seek out that amulet in the ancient ruins. I know all about you and your deeds, because I am just another random NPC used by the DM to interact with you."

Yeah, I know the response, "But that is railroading!" Or maybe it is not. Maybe the players have taken a break for a time and don't quite remember what their characters were up to. Maybe its been 3-4 weeks due to Finals, Christmas, New Year, and whatever, since the whole group got together.

And yes, you could rehash it all out of game, but some folks actually like to, you know, roleplay, as crazy as that is, I know.

Which brings up a thought. In the two groups I game with, the one group that uses the pronouns "I and me" most often is also the one that doesn't roleplay very much. They don't have characters they have proxies. Their characters are as significant as playing the boot in Monopoly. The other group that actually roleplays their characters as individual characters separate from the person playing it are more likely to say "Darken does ..." They still say "I" and "me" as well but the other group uses those pronouns exclusively where the roleplaying group varies from time to time.

You can have a love of roleplaying and not think that everything related to the game needs to be described in-game.

In the cases where you're claiming that a DMPC is beneficial, it'd be quite a bit more immersion-breaking for these people to forget what they're doing with their lives. Talking things over OOC before the game is the only way to maintain sensibility.

pres_man
2012-03-17, 03:21 PM
In the cases where you're claiming that a DMPC is beneficial, it'd be quite a bit more immersion-breaking for these people to forget what they're doing with their lives. Talking things over OOC before the game is the only way to maintain sensibility.

"Only way"? Ok, gotcha.

Mystify
2012-03-17, 03:23 PM
I say that if you can avoid the pitfalls and do it properly, it adds to the game. It may not be appropriate in all groups and campaigns, but that is part of using it properly. Going to the culinary analogy, I once had a great peice of cloud 9 cake. Its basically a piece of chocolate cake surrounded in white chocolate mousse, with a raspberry sauce. Together, it was amazing. However, if you tasted the raspberry sauce by itself, it was quite bitter. Putting it on most things would not have worked. But in that dish, it was the perfect compliment.
Its not a case of "oh, I think I'm a good enough DM to pull it off, I should add one in.". Its a case of "This campaign could be really helped by a DMPC".
For instance, the proxy for the artificer I mentioned earlier. Even in retrospect, I think that I made the right decision on how to handle it. Without the DMPC, that campaign would have been worse. Using a different approach to that situation would have yielded worse results.
Other cases, you can do it with a neutral effect on the players, but vastly increase the DM's enjoyment. For example, in the one I saw the DMPC done well, I can't say that the DMPC really exerted much of an influence over the game, beyond a proxy for the DM to make (appropriate) comments on what we were doing on occasion. But, it also allowed the DM to partake in the enjoyment of trying out making a character in the system. The net enjoyment of people at the table increased, and so it was a good thing.

Sucrose
2012-03-17, 03:28 PM
"Only way"? Ok, gotcha.

Yes, because the alternative is that Bob the Fighter forgets Greg the kitten-killer's name an hour after promising to hunt him down, if you have a break large enough between sessions.

PersonMan
2012-03-17, 03:34 PM
Cake and sauce analogy.

I think that food is a fairly good comparison.

If you know the people eating the meal do not like a certain kind of sauce (DMPCs, or whatever you call them that isn't automatically negative), then it's a bad idea to use it.

If you know the people eating the meal are fine with a certain kind of sauce, if served on the right dish, then it depends on the dish. You should ask them before making it, though, as they might have different opinions of specific kinds of dishes or have past experiences that make enjoying the dish impossible (an uncle of mine ate too much of specific kinds of food when he was younger, and now eating those kinds of food just doesn't work for him).

If you don't know the opinion of the people eating the meal on that specific kind of sauce, then it's a good idea to ask them if you're thinking of including it (assuming that you know that the dish is appropriate).

The sauce, if applied incorrectly, can ruin a meal (I can vouch for the ability of a single component to screw up an entire dish). If applied correctly, it can spice up the dish a bit.


Yes, because the alternative is that Bob the Fighter forgets Greg the kitten-killer's name an hour after promising to hunt him down, if you have a break large enough between sessions.

Instant counterpoint: Bob the Fighter's player wrote the name down at the last session.

pres_man
2012-03-17, 03:36 PM
Other cases, you can do it with a neutral effect on the players, but vastly increase the DM's enjoyment. For example, in the one I saw the DMPC done well, I can't say that the DMPC really exerted much of an influence over the game, beyond a proxy for the DM to make (appropriate) comments on what we were doing on occasion. But, it also allowed the DM to partake in the enjoyment of trying out making a character in the system. The net enjoyment of people at the table increased, and so it was a good thing.

I think you are touching a good point here. Roleplaying isn't a zero sum game (or rather I should say it doesn't have to be, from some of the comments I've seen here I am sure that some folks certainly do approach it that way). One player's ability to enhance the experience doesn't necessarily take away from another's. A DM run character having stage time may actually enhance the stage time that other player's characters have. Game time is as much about quality as it is about quantity.

pres_man
2012-03-17, 03:44 PM
Yes, because the alternative is that Bob the Fighter forgets Greg the kitten-killer's name an hour after promising to hunt him down, if you have a break large enough between sessions.

Because a person has never been introduced to someone and then 5 minutes later totally forgotten their name. LOL
"Only way" LMAO

Coidzor
2012-03-17, 03:45 PM
I think having a constant character that the DM can use to interact with the party in game and in character is of some benefit in a lot of situations. If a different random townsfolk in each town that the party comes to know exactly what is going on and can remind them why they are there, that really breaks the immersion for some people.

If they're the kind to care about immersion and they can't remember what they're doing in game from their own notes, they deserve the irritation of having an out of character conversation. :smallconfused:

pres_man
2012-03-17, 03:48 PM
If they're the kind to care about immersion and they can't remember what they're doing in game from their own notes, they deserve the irritation of having an out of character conversation. :smallconfused:

If they didn't study for the test, then they should fail. Because gaming is just liking going to school. Better make sure you take good notes or the DM is going to flunk you. LOL. What a blast you guys must be to game with.

Sucrose
2012-03-17, 03:59 PM
Because a person has never been introduced to someone and then 5 minutes later totally forgotten their name. LOL
"Only way" LMAO

If you are promising to hunt someone down, you care deeply enough about their sins to remember their name. That you ignore this and choose to act like I'm talking about an acquaintance, twisting my words to make them easier to defeat, is a textbook strawman argument. Please stop trying to do that.

Coidzor
2012-03-17, 04:04 PM
If they didn't study for the test, then they should fail. Because gaming is just liking going to school. Better make sure you take good notes or the DM is going to flunk you. LOL. What a blast you guys must be to game with.

If they're that much for immersion then they should logically be taking steps on their own. So, yeah, your example is kinda... incredulous.

ko_sct
2012-03-17, 05:28 PM
Personally, I never take notes, nobody does it in my group, if someone doesn't remember what happened last session (which can be last week, or 6 months ago, as was the case once) we simply discuss what happened, no need for notes or random NPC coming to tell us why we are in the middle of the astral sea and what we are doing.

We do care for immersion but not much for taking notes, nothing very special there.


On the subjects of DMPCs, we have been using ones frequently in my group for years, it has almost never caused any problem, and never had a major problem with them.

Some say that because the DM know everything, the DMPC will never make a bad decision, I disagree with that. When I game as a player, I often make suboptimal or bad decisions for my character because it would be more interesting or because my character shouldn't know any better (like knowing a monster weakness but not using it because my character shouldn't know about it) if I can do that as a player, I shouldn't have any problem doing the same as DM, right ?

Mystify
2012-03-17, 05:49 PM
Personally, I never take notes, nobody does it in my group, if someone doesn't remember what happened last session (which can be last week, or 6 months ago, as was the case once) we simply discuss what happened, no need for notes or random NPC coming to tell us why we are in the middle of the astral sea and what we are doing.

We do care for immersion but not much for taking notes, nothing very special there.


On the subjects of DMPCs, we have been using ones frequently in my group for years, it has almost never caused any problem, and never had a major problem with them.

Some say that because the DM know everything, the DMPC will never make a bad decision, I disagree with that. When I game as a player, I often make suboptimal or bad decisions for my character because it would be more interesting or because my character shouldn't know any better (like knowing a monster weakness but not using it because my character shouldn't know about it) if I can do that as a player, I shouldn't have any problem doing the same as DM, right ?
I've had a TPK due to the player's role playing their characters ignorance of vampires.

Knaight
2012-03-18, 12:48 PM
Is there a dish that gives food poisoning sufficient to make you violently ill, but likely will not kill you, unless prepared with about the same care as fugu? That'd be closer.
There are several dishes that involve raw red meat. You'll survive eating bad raw red meat most of the time*, but the next week or so is going to be miserable.

*If you have a particularly bad immune system or similar this would be problematic.

Coidzor
2012-03-18, 04:43 PM
Amateur steak tartar, perhaps?

navar100
2012-03-18, 10:05 PM
Our NPC cleric heal bot died this past game session. I guess that proves she wasn't a DMPC. :smallsmile:

:smallfrown: for the passing. We'll miss her.

Coidzor
2012-03-18, 10:25 PM
Our NPC cleric heal bot died this past game session. I guess that proves she wasn't a DMPC. :smallsmile:

:smallfrown: for the passing. We'll miss her.

If all it's doing is serving as a healbot, that would suggest against it in the first place, yes, since very, very few people actually enjoy that.

pres_man
2012-03-18, 10:29 PM
If all it's doing is serving as a healbot, that would suggest against it in the first place, yes, since very, very few people actually enjoy that.

Still it would not be proof against it since, though few people would enjoy that, those few would actually.

I have seen the same argument made when someone says, "My DMPC just hangs back and goes with the whatever the group decides, not pushing any personal agenda." And some responds, "See, then it isn't a PC, because PCs don't act that way." But some people, who are not DMs, actually do run characters that way. And they are just as much a PC as the person who takes on the leadership role and decides where the group is going to go and what it is going to do. There are leaders and there are followers, there is nothing wrong with either.

Coidzor
2012-03-18, 10:31 PM
Still it would not be proof against it since, though few people would enjoy that, those few would actually.

I said "suggest," good sir, did I not?

Killer Angel
2012-03-19, 03:53 AM
There are several dishes that involve raw red meat.


Amateur steak tartar, perhaps?

Or carpaccio (http://en.wikipedia.org/wiki/Carpaccio).

pres_man
2012-03-19, 04:43 AM
I said "suggest," good sir, did I not?

Yes, but I was just trying to point out the statement seems a strange one to me. It is like saying that a character isn't really probably a PC because it is a monk and most people don't like to play monks. The fact that most people don't find something fun doesn't mean it isn't a totally reasonable way to play as a PC. The fact that the character was a "healbot" doesn't make it any more or less likely to be a PC, than say if it was a monk or any other non-popular character choice.

Coidzor
2012-03-19, 05:39 AM
Yes, but I was just trying to point out the statement seems a strange one to me. It is like saying that a character isn't really probably a PC because it is a monk and most people don't like to play monks. The fact that most people don't find something fun doesn't mean it isn't a totally reasonable way to play as a PC. The fact that the character was a "healbot" doesn't make it any more or less likely to be a PC, than say if it was a monk or any other non-popular character choice.

Really it's mostly because it's not really doing anything if it is a "healbot." It's like a bloody pet rock or an ambulant wand of cure light wounds. At least a monk is flailing uselessly about like a gutted fish.

That, and it is a noted non-DMPC practice to include an NPC healer ally that doesn't do anything more than be window dressing outside of healing wounds out of combat and maybe stabilizing people in combat.

And if their idea of fun is not doing anything... how are they DMing? :smallconfused:

Musco
2012-03-19, 07:59 AM
I have fallen into the DMPC trap before. In 3.0, I was just starting DM'ing, and I actually had one as both a female view for the party, which was all-male, and as a safety net, in case I missed playing.
When I ralized I didn't, I actually killed her off in an epic fight they were in, by having her jump in front of a spell that'd have obliterated the party Wizard had it hit him. He was the character - not player - who actually openly disliked her, too, which created a very interesting dramatic point from there, since his character never forgot the sacrifice (it was not possible to ressurrect her due to story-line issues).

Nowadays, I don't miss it at all, and have gone full-blown DM with no characters whatsoever for quite some time.

That being said, we're picking up 4.0 after a long debate on wether or not to upgrade, and I have built a character yet again, since the group I was DM'ing for disintegrated due to a problem with a player (both in-game and outsite of it), and the leftover players simply did not have a defender anymore - and boy, do they need one! -, lost an important source of healing, they are all ranged-based and they now have a Warlord tailored for teaming up with melee heavy hitters with no one to team up with, so I went ahead and built a Paladin, to shore up all their needs for the moment. I actually tied his storyline to one of the characters that left, so he's basically a character that was already there, just slightly different (and of course, less of a jerk, a problem another player had - I stress "player", because it was not a character thing, otherwise it'd have been fine).
They are all fine with it, since they'd rather hold on to their characters for now (it's really early on the campaign), and I worked the guy to be reclusive enough that he does not steal the spotlight but still has a goal (and the party is well aware of it, due to him being related to one of the guys who left), and the moment I see he's not needed anymore (they shored up their weaknesses in some other way, like MC'ing, magic items or even someone building a new character for whatever reason), he's ready to go away.

Another selling point is that, as mentioned, the group is new to 4.0, and they're not very good strategists as well, so by "playing" a defender, I can show a little battle strategy (positioning, snap judgments about dangerous enemies, inventive strategies, BAD strategies - he will mess up sometimes, of course - etc.) and battle roleplaying (talking in character during combat, relating to taking hits and hitting, emotional responses, etc.) to them without hogging the spotlight (lesser damage output), which I think is actually a good argument in favor of it, as a way of showing possibilities in-game to players without actually discussing it openly in the middle of a game session.

Serpentine
2012-03-19, 10:33 AM
A DMPC is fundamentally unfair. Its never going to accidentally step on a trap. It's never going to overestimate or underestimate enemy forces. Its never going to wonder whats behind that door or who the murderer was.My DMPC would do all those things.

The players will never see the DMPC as 'one of us.'My players do.

Furthermore if I have an argument with Wizard Bob that's fine. If I have an argument with DMPC John I'm also having an argument with the guy who could declare my face melts off, no saving throw, no roll for initiative.My players have had disagreements with my DMPC. They've played tricks on her before. It's entirely possible that they would have a big argument with her in-character - she's Lawful and there's a significant Chaotic element to the group, after all. If I thought at any moment that my players thought that I would melt their faces off just for doing that, I'd give up DMing forever.

#1 DMPC does not provide a satisfactory play experience.Mine does, and I'm sure there's plenty of others who have too.

#2 DMPS only does well in a support role, which could have been filled by NPCs.What's the difference between a well-fleshed out, backgrounded, personalitied NPC who follows the party around and interacts with them as a fellow useful party member and is run by the DM, and a well-fleshed-out, backgrounded, personalitied, fairly run DM's PC who follows the party around and interacts with them as a fellow useful party member and is run by a fair, self-aware DM?
In all seriousness, without getting into the whole "DMPCs are bad by definition" thing, I don't see the difference in practice. For one, you have a character run by the DM hanging around the party being useful and interacting with the other characters. For the other, you have a character run by the DM hanging around the party being useful and interacting with the other characters. The only difference is the DM's sense of ownership - which, to repeat myself, does not lead inevitably to favouritism and immortality and so on. The only practical difference, assuming that latter point, might be that the NPC is boring and lifeless thanks to lack of DM interest. That doesn't seem like a bonus to me.

I don't know if I've made sense here... To attempt a quick summary, if I had to make a choice between an NPC and a DMPC to fill a party role in the long term, I don't think there'd be any real difference between the two characters. I've just spent a minute thinking about it, and I can't think of anything. The party decides to pick up a random Cleric to help out with the undead they're pretty sure they'll be running into? I'll give the Cleric levels and experience, I'll build them as I would any other PC with all the same restrictions (I suppose I might be very slightly more likely to give the NPC version some sort of "Get Out Of Gaol Free" card in case the party gets into trouble), I'll give them the same personality and background and knowledge and chance of clashing with PCs as I would if I'd made a DMPC for myself.

And when used well--they don't hurt anything but don't add anything of value, either.My players disagree.

killem2
2012-03-19, 11:44 AM
I'm with you Serpentine, a lot of that you just quoted is biased, unsubstantial opinion.

Just to put some of the haters to rest, we finished our third session, with my level 3 focused evoker.

Just like the first two sessions, it was a blast and they loved it. They really appreciate the magic side of things. I'm pretty low profile, I don't hit that often even with the bad ass spells, like seeking ray.

We had one hell of a tactical blow out. We had:

Level 3 rogue, wizard, cleric, fighter, ranger, and the fighter's gaurd dog, and rangers elven hound, and my wizard actually has a growing bear cub. The bear isn't much though.

Because of reserves of strength I knocked out 7 of the 20 orcs that we flanked in their own base. (room had multiple ways to enter it.)

The also love the transposition spell. To those who make this out to be such a big f'ing deal, really need to find another game to play, because obviously this is too challenging for you. It isn't hard to just play the turn as if you were a player, and unless your players are complete idiots, they should learn fairly quickly not to rely on your interactions with social events.

When i give a guess at a solution, I just talk as if I'm talking about my character. I think this is just one of those stupid things that trolls feed on and no one can ever discuss it like a rational human being. If you did, you'd realize you were against something that can be actually really really fun and helpful.

Serpentine
2012-03-19, 01:07 PM
Oh shoot, you just reminded me that we have at least one baby roc and a whole stack of eggs I don't know what we're going to do with, and that I really don't want the party to forget about...

Not relevant, I just got reminded :smalltongue:

Bebo
2012-03-19, 02:02 PM
From all of the previous posts, it seems this debate comes down to the issue of intent.

The DM that is playing with a smaller group and creates a support character with the intent of filling holes in the party, or the DM that is playing with a group of new players (or playing a new system) that creates a support character with the intent of helping the group learn the game by example seems to have success with the DMPC.

The DM that would really like the chance to play as a PC, but cannot find anyone else to DM, and so creates a DMPC with the intent of having a player's experience seems to fail.

The first group of DMs get their enjoyment by helping their players, so everyone has fun, and no one objects to the DMPC.

The second group of DMs try to get their enjoyment as a player, and if they don't have fun (which from the stories presented here, most in this camp don't), then no one has fun, and the players hate the DMPC.

The only other issue here is one of semantics. Group 1 likes the DMPC concept because it works for them, and have no issue with the term DMPC. Group 2 hates the DMPC concept, and consider the support characters played by Group 1 to be NPC allies, cohorts, etc., which for them is not a DMPC.

So, can anyone "win" this debate? I don't know. But I think we can all agree that we would rather play with a good Group 1 group, where everyone has fun, than with a bad Group 2 group, where no one has fun.

Karoht
2012-03-19, 02:31 PM
Semantics are semantics. I greatly disenjoy semantic/pedantic discussions for the most part.

My DMPC example really only existed because I was unaware of the existance of the spell Spiritual Ally or Spiritual Weapon, and I wanted to give the player party an item that functioned mostly similar. It ended up being the reason for creating a bunch of backstory and a load of sidequests that sort of ended up being a major quest. I guess it evolved away from being an item-based DMPC and into a major NPC.

But lets say it hadn't evolved that way, and remained a DMPC that only came out to play when the party needed it, at the party's request.

I think as long as the player party has the ability to tell the DMPC to shoo, or for the party to be able to call upon the DMPC when they need it, isn't really so bad.

Deepbluediver
2012-03-19, 03:32 PM
I think, like many things, the value of a DMPC can be described by the phrase "...when done well".

The issues for every group are different, depending on it't size is and what strengths and weaknesses the players have, and what the DM is trying to accomplish. Frankly, I think that the potential for problems vastly outweighs the potential for benefits, and DMPCs should be avoided whenever possible except in limited doses.

Calzone
2012-03-20, 12:18 AM
I might be blurring the line between what people think of a DMPC and "party NPC" - I will call it a DMPC, but I'm using the definition "DM-controlled characters who adventures with the player characters as one of them for an extended period of time."

One thing I think a DMPC would be good for in a small group (my typical group is two other people) is to serve as an in-party foil to a PC. Basically, I'm thinking of a way for small groups to replicate the type of character development you get by having player characters with conflicting archetypes or motivations interacting for a common purpose. (think playing Watson to Sherlock Holmes, scallywag to honorable knight, etc.)


Upsides:

PC(s) being contrasted get to show additional aspects of their character that would normally only get play in a larger group
DM gets to play a character with more nuanced role play opportunities than a random shopkeeper or monster.
The DMPC has more DM-PC interaction than DM-DM interactions



Caveats:

DM must be willing to play the part of the foil - his interactions exist to draw attention to particular aspects of the player character(s) personalities. (ie, no power-tripping DMs! Use your BBEG for that!)
This DMPC role is meant to fill a character development role your existing players don't want to or can't fill (ie, you have Sherlock Holmes and Davy Crockett adventuring together, and Sherlock wants a Watson). If a PC wants to be a foil, let them do it instead of you.
More so than most DM tools, this is very play style specific - Make sure your players are looking the more character driven role playing this suggestion expects.