My suggestions, coming from the other side of the fence where I (and some of the other players) feel that the DM plays a little too fast and loose with the rules, and makes changes to things that we think ought to be "canon" for the well-known world we are playing in:

1) Be willing to consider that the player may be right. Allow him to make a breve argument referencing the rules. Then make a ruling. Make a mental note of how often you rule against the player versus how often you change your mind and agree with him, and try (later, outside the session) to assess whether you're being particularly harsh and/or truly weakening one character's abilities relative to the others'.

2) Be firm if you still disagree with him. If he still disagrees with your ruling, tell him, "I need to ask you to go with the DM ruling for the moment and we can discuss it more later outside of game time, to figure out how we'll play this type of situation in the future."

2a) Try to offer the player another way to reach his objective. Say something like, "Look, the rules say that you give away your position if you attack from hiding. If you then, in full view of the enemy, duck behind the same tree, they are going to know where you are, even if you are so well hidden that they can't perceive you. Thus you do not get the advantages of being hidden in that case. Now if on your next turn you stealthily move to the next tree and hide there without being noticed, and then attack, aquele would be unexpected and give advantage."

3) Ask players not to use the Monster Manual at the table, and to avoid using metagame knowledge about monsters. That said, try not to mess with well-known monsters in a canonical setting without a really good story justification. If you're playing in a canonical setting, Mummies are going to be something that most adventurers will know the legends of, and the way that Mummies are described in this universe really does preclude a "good-aligned Mummy". If there's going to be a good-aligned Mummy, there should be a good story to go with that, to say how that happened contrary to the usual Mummy creation process, that the PCs have at least been given hints about. Otherwise, yeah, it's pretty appropriate for a PC to automatically kill any Mummy he comes across on sight. They will know the stories....

Note that the 5e MM does say (page 7 if need a reference for your rules lawyer):

The alignment specified in a monster's stat block is the default. Feel free to depart from it and change a monster's alignment to suit the needs of your campaign. If you want a good-aligned green dragon or an evil storm giant, there's nothing stopping you".

However, unless there is a good story behind the anomalous alignment, and your PCs have access to clues about that story, I think it would usually be better (and annoy your players less) if you either make up a new monster that isn't in the MM, or be clear that you are playing in a non-canonical setting and using monsters that don't match the descriptions in the MM. Even in a canonical setting, you can play variations on less-legendary monsters, but be clear (out of character) with your players that this is what you are doing. In all cases, allow the players relevant checks to recall some in-game, in-setting lore about the monster you are actually playing.

For example instead of just putting in a good-aligned Mummy you could say, "You see a medium-sized humanoid, wrapped in bandages. Make a religion check". Tell everyone with a low score that they think it's a Mummy. Tell whoever got the highest check, "Because of [some detail that they can perceive] you think this might not be a true Mummy but rather a Pseudo-Mummy. Pseudo-Mummies are created by a different process than True Mummies and in some cases can maintain their pre-death alignment." If you want, you can go into the process more, or you can just say that the character doesn't know any more than that. Now you have a good-aligned Mummy that your player shouldn't complain about.

4) Consider having a talk with the players about what game everyone wants to play. You have a conflict in play style with the "rules lawyer" player. Do the others also want to play "his" game, or do they prefer your approach? Can whoever is in the minority live with adjusting their expectations to what the group as a whole prefers? Can there be some compromise?

So I too had a player and friend who was exactly like this in my games. The tactic I used to eliminate this problem was rather simple:

All rulings are DM rulings, and arguments that grind the game to a halt are relegated to after the game. If he persists in pressing an argument after you say, "Discuss this after the game," then just turn to the other players and ask them what they are doing while he argues with nobody.

If he makes it a habit of going into the monster manual for stats, start modifying creatures in small ways to throw off all expectations and discourage the meta-gaming behaviour.

Most importantly, talk to him about the three types of rules. RAW, RAI, and RAF. The last one is the important one. Rules as Fun is the DM perogative to making things interesting and thinking outside the box. If the player persists in being a detriment, everything comes down to telling him to either fall in line or he is not welcome at future games.

Rule lawyering is a start to playing D&D, but it certainly is not the goal. Its just the framework for a system that is supposed to encourage creativity and imagination.

Now, as a side note to the examples you posted above:

1) Stepping out from behind a tree, firing, and then using his Cunning Action to hide again is a creative and interesting way for him to remain hidden while firing. Consider the Intelligence of the creature he's firing at, and whether or not it would pay special attention to the area the arrow came from should a second shot be loosed from there. What I'm saying is consider compromise when players do creative things like this.

2) Passive stealth is not a thing.

Stealth. Make a Dexterity (Stealth) check when you attempt to conceal yourself from enemies, slink past guards, slip away without being noticed, or sneak up on someone without being seen or heard.

There are two kinds of rules lawyers, and the way you treat each depends on where they sit between "I know the rules and want to help" and "I know the rules and will use them to break the game in my favor".

The first type is the helpful one. They usually know the rules from heart, or at least know where they should look for an obscure rule. They are not trying to harm you game, but just trying to keep the game world consistent. If you say a standard ogre tries to jump over a 20' wide river, he will point to you that he needs to make a check of DC 99. If you say "no checks, he jump because he has an ability for that", he mighty think you are cheating, but will go on with the game. And if you put other river-jumping ogres in the future, he will just assume that is the new status quo, and that is no big deal.

You can identify the first type easily when he calls out a rule that have the potential to hamper or harm the party because of consistency. That are stuff like:

"You need to roll 15 to pass this check" Rolls 16 "No, wait. I forgot that we fell in that hole full of unspeakable earlier, and I have -2 on this check. Dang."

The second type don't want to make a good game. He don't want to help everyone with their game knowledge. They want everyone to remember every rule that benefits him, and while he poder not complain when a rule will cripple his character, he will not be as eager as before to remind you of that crippling rule. In some rules with confusing wording, he might even twist them differently depending on which situation he is facing right now in the game.

"I know I said last week that dim light give you a bonus to stealth, but we are carrying torches, and that nullifies the dim light penalty, and thus, the monster should not ambush us."

The former is a good addition to every table. You might disagree with him, and tell him to shut up when he goes into a vast monologue about why a minor rule exists, but most of the time the intention there is to help.

But looks like your player is from the latter type. Then the problem is not exactly his rules lawyering. The problem it that he don't like when his character can't do everything he wants him to do, and he is willing to distort the rules to make them work like he wants (Seriously, passive stealth?).

My advice to deal with such players is kinda short:

• Take a non-game day and have a talk to him. Put on the table everything you think is wrong with his rules lawyering. Give examples. Be clear on the feedback. Then ask him why he does that. And try to reach a consensus of when is the right time to decide such rules.
• Next time he wants to give you information about a rule, ask him which page from which book. If he is capable to show you it quickly, then he is right. Accept and keep the game running. If he starts to take too long searching for the rule, then says "I will rule that this way. If you find the rule, tell me after the game, so that we might use the proper rule next session."
• Be consistent. If you ruled that you can't hide behind the same tree you just left, then this should be the rule from now on. He can't use this trick, and neither can you. If you have the tools and/or ability to do so, make a small note on every ruling call you make while running a game. After the game, read them and look out if there is a rule for those. If not, keep the notes. You need to be consistent. While you are consistent, they can't complain about you breaking the rules.

There's a difference between someone acting in good faith vs. bad faith when it comes to rules lawyering - and the sign is how they react when the same rules are used against their character. The good faith player goes, "Oh yep, you got me! Damn!" and keeps having fun. The bad faith player then argues the rules don't apply or pouts and is angry. In other words, one person actually cares about the rules as an accepted part of play, and the other only cares about things going their way.

Now, if you've already spoken to the player about what kind of game you want to run, and they're not interested in it - what's in it for you, or them, for them to keep playing? You say kicking them out is a "last resort", but honestly, after you've spoken to them, and both of your positions are clear, what else could happen?

An unfortunate question to consider is this: if the player doesn't want to play the way you want to run the game, why are they still there and what's in it for them? Some players like to push the group around and take the spotlight. They como to argue. They're not really there to play the game, and the fun they're getting has nothing really to do with the fun the group is trying to have.

By all accounts of what you've described, it doesn't sound like this is a matter of misunderstanding or miscommunication - this "one of the best" players you describe doesn't seem to bring anything valuable to the kind of game you're running.

I as a GM handle rules rather loose as well, and would probably have reacted somewhat similar like you. But over time I had some players that had similar "problems" and talked with a lot of other GMs about their groups that had similar "problems" and with that I'd recommend you to the following:

Think about the situation objectively and try to value what you as a GM want and do and what the player wants and does. And then talk to him outside of the game. As talking is the only way to find a solution that both of you can enjoy.

Things I'd recommend to keep in mind while thinking about it:

• It seems that the player sees the GM as an enemy. Don't take that personally. It's unlikely to be a personal thing, but probably just the way he likes to play. He sees the game as a competitive fight against the GM and within that fight you're the enemy. And the battlefield are the rules. Thus he wants you to handle the rules strict to the book, because otherwise he'd be in an impossible fight. From your questions it's obvious that you don't see it as a fight, player vs. GM, but you should respect the fact that he sees it like that. Don't try to force him out of it, but convince him to come out of that position and come to a compromise.

• You both clearly have different expectations from a game. He prefers to fight. You probably more story and role play based. None of them is right or wrong. Thus don't think about what he does as wrong. The way he plays is not wrong! It's just different than yours. Thus you should clearly think out what you want from an evening of RPG, as a GM, and compare it to what he probably wants. Find the differences but find the things you have in common as well.

• If you know what you want and what he wants, think about what you can offer him. If rules are so important for hi, try to stick to them more strictly. Or if you bend them, clearly tell him "I bend the rules. And this is the way the rules are now...“

• In all the situations you described he was on the defensive. Basically you told him "no, your way of playing in this is wrong". So try to talk in a situation, where you meet on an equal base and can talk without being offended. Before you start talking, he has to know, that you don't want to fight him about the rules, but want to find a way that you BOTH have more fun. Give him the feeling that you both work on a better evening of RPG, so he's willing to work on it as well.

• I'm usually one of the GMs that says "I'm the god in this World and I make the rules. Live with that". Up to now that worked well. But I can't expect the players to just go with it. I might be the god, but they are not my puppets. They are the Main characters in the world and I'm to form the world around them. Thus I have to give them the role of the Main characters. I can't just tell them a great story, because it's not just about the story. I can give them the settings and the start of the story. But they write the story. They make things happen. And thus they have to be in charge of that AND know that. Esp. in a classic fantasy RPG the Player have to feel that it's their story and they live it.

• If he's so comfortable with playing D&D cause he knows so much about how it should be: try playing a different game where he doesn't know the rules that good. Try to turn it away from a fight based on rules but turn it into a fight where he's good, cause he has good ideas or where he as to work with the other players to "win". And clearly tell him the reason you want to do so. Let him know that you want to do it to improve the fun he has in the game as well, rather than just taking away his weapons of choice.

There is one story where I was as a Player under a GM that taught me a lot, how a GM can do it wrong. It led to a lot of trouble in our usual group when the GM started to do it more often and I as a GM myself tried to learn from it, what not to do:

We were playing Shadowrun and had a mission to do something for the Dracofoundation. A Company that mostly based in meta story you get from books and has not a lot to do with "normal" Shadowrunners. But the GM liked it and we were ok with having them as a Johnson. We just wanted to have a good run on a funny evening. But in the end it really backfired as the GM was so focused on the Dracofoundation, that we wanted it to be a major role in evening. In some situations he more or less wanted us to report to them, what happened. But we didn't want to do so. Thus he just made them notice it anyway and they contacted us like "we just notice what happened. Here is what you should to about that." In the end it turned out that a lot of the Shadowrun Meta-Story was built into the plot of the evening and the make some known names from the Dracofoundation come around as cavalry and solve the plot in the end. Couse he though they are cool and it's awesome to have them in the story. While us as player were pissed. 1) We were thrown into a story with characters that are way stronger than us and didn't felt it fitting for our characters that we even me them at our level. 2) Cause we didn't want to solve the story he wanted us to we were reduced to the sidekicks while the awesome guys solve the problem. That felt really bad and took away all the fun.

In the end I learned that as a GM you can't just tell a great story and force that on the player. You have to tell THEIR great story.

In your case: You might be really good in telling a story as a GM and have a lot fun with it. But that player might not enjoy it as a story, if the story doesn't go by the rules he expects it to.

And one last thing: Don't say "kicking him out is the last choice." It might just be that you and him as GM/Player can't work together, no matter of how good you get along otherwise. In that case it's better to remove him from the group or spilt the group up than create more upset about it.

I am at a loss, does anyone have any experiences with players like him?

Yes, I have had that kind of experience. Most people who DM eventually run into one.

What's the best way to handle it?

That depends on you and your circle of friends / gamers. Interpersonal relationships are complex and dynamic. A leisure activity leading to friction can harm friendships. (Seen that more than once, and it's sad when it happens ... I've seen it happen in golf clubs as well).

Besides first getting a grip on your relationship --- friends, close friends, just gaming friends, something else --- be sure of one thing ...

That key first thing:

You need to know the rules, which in 5e certainly means know that PHB very, very well. The better you know them, the better your rulings are, the better grounding any of your rulings has.

Second thing you do:
(This is in the social contract category of things)
Establish a rules question interaction tool for your table (our current DM did that for our group) and then stick to it. Any DM can forget or confuse a few rules, so it's not inherently bad for players to explain why they think it "ought to go deste jeito."

Best way I have seen as both player and DM:

DM: Make your case ... case made briefly ... DM listen ... DM makes ruling. Play now continues. (Our current DM is very, very good at this).

Getting the group to buy into this tool is core, and touches on a fundamental bit of table courtesy: we are here to have fun, not get into emotional arguments nor personal attacks.

Harder part: once the rule/point is found, making the resolution timely. Your interpersonal relationship with the person making the challenge may end up with taking on the character of a test of wills. Try to make your appeal, to the whole table, to your agreed tool mentioned above.

While these are clumsy words that follow, they capture the point to make to your gaming friends:

"Folks, it isn't fun for this fun game to not be fun for the GM (who is allowed to have fun). Having it turn into a pissing contest with a friend when we should be having fun playing together is not fun."

Take from that what you will, but GM's are allowed to have fun too. Getting grief from players hurts fun.

With this player, it looks like you need to address this problem in private before your next gaming session. He needs to know he's damaging the fun of other people in his pursuit of fun. He may not see it until you bring it up.

An option, but one that may not work in your group:

• If you think it necessary, you can allow only one set of books at the table, which you retain custody of. (I never liked that, been at numerous tables where it was the rule ... it is an extreme step among friends/adults).
  • The physical act of "here's the PHB, take a look, you have X time ... and while you do that Player A is doing ... what?" puts a little control in your hands. It can help keep things from stalling.

See also this q/a on a related topic about the DM being right. If you think some of that makes good sense, share it with your friend - rules lawyer - player.

One option I haven't seen stated in the previous answers might or might not work for your particular case, but I have found that it can change the perception of a rules-lawyer "munchkin" player a great deal.

In some of my games, I have found that the psychological paradigm set up by the DM being the adversary brings out this kind of conflict. (You have to remember that as the DM you are literally THE antagonist to the players in everything they do, so inexperienced players can shift their focus from the in-game enemies to you, which seems to be happening here). I have found that sometimes, when nothing else works (and I am skeptical of the "take him aside and talk to him" approach, since he sees himself as your opponent at the table and there is no reason for that to change when you are alone) I set up a "guest DM" session. I would "pause" the main campaign, have everybody roll up a few expendable new characters just to mess around with, and let the rules lawyer get a taste of being DM for a change. Short, pre-packaged adventures work well for this type of thing. Just doing this once in a while (usually rules lawyer type players don't have the stomach for the research and preparation required to be a regular DM) can change a player's attitude a lot.

Suddenly, sitting on the "other side of the table" so to speak, the player realizes that problems are not always clear cut, rules don't answer most questions that come up, and being "fair" is often a real challenge. He may come away with a newfound respect for you. Alternately, he may use his time as "guest DM" to mercilessly and unfairly destroy your expendable PC! I've seen it go both ways, but even in the latter case, at least the rest of the group will quickly realize that this is more about his problem with you personally than an issue with how you are running your game in general.

I must challenge the very premise of the problem that the problem lies with the player who is dejected... rather than with the GM who caused the dejection. Also challenge the assumption that rules "lawyering" is the cause rather than the symptom.

Consider the consequences of your rulings. By ruling that their rogue cannot use stealth in so many circumstance means then they can't sneak attack. Rogues are all built around that. I know you were acting reasonably, of course it's not unreasonable that you consult your intuition and your intuition will tell you "of course he can't still be hidden, the stealth check fails".

But a GM's job is not to be a mere arbiter of intuition or common sense, a GM has a duty to craft an enjoyable game. The problem isn't with you ruling differently than the rules, the problem is with you ruling then differently in way that is in such disregard for what makes an enjoyable game. If there's going to be any ruling differently from Rules-as-written it should be in favour of fun. Rule of cool.

This is related to My-Guy-Syndrome only now the GM is the culprit. Now it's a case of "well my guy wouldn't miss him" you can just as easily have the target of the rogue be confused, arrows seem to be coming from nowhere as they scan around and are looking the wrong way when they are shot in the brief moment the rogue pops out of cover.

Characters like a Rogue are a challenge for a GM, you are obliged to cater to their need for stealth and the other aspects key to triggering sneak attacks. It would be like if you had a melee fighter who was constantly attacked by flying creatures with ranged attacks.

And while you may have had particular plans for that Mummy, it may again be that the rules are a symptom, not the cause. The symptom of the GM failing to properly foreshadow that this Mummy would be so different. A GM should entirely expect that a player would be fearful and mistrustful of an undead abomination, the rules book wouldn't just tell him that, any rogue who lived in that world would fear the undead. They shouldn't even need to resort to the rules to back up their decision there, as far as they knew the GM was tricking them or it was an obvious threat.

Remember, Mummy attacks are VERY debilitating, you are expecting them to trust this character you plopped into the world, you are going to have to do muito to earn the trust of each and every player around the table. You aren't looking at the game from their eyes. You're telling them to risk Mummy Rot.

I know this can seem overwhelming but one thing you can do if there is a dispute with the rules is learn this phrase:

"Well I don't know, but desta vez it goes like this"

and leave your ruling up in the air for now if you REALLY don't think that stealth check should succeed. That's part of the problem here, in the heat of combat players feel like all future rulings is going to refer back to this snap decision. This puts the pressure off everyone, the final ruling can be deferred for later and if in retrospect you decide "well actually if I don't count things like this for stealth it's going to really suck being a rogue" then you can reveal that the tree actually had a hole in it all along that you hadn't noticed and in that rare occasion, he could still locate you.

And once they end up attacking the Mummy, cut your losses, accept that you failed to make it clear that this Mummy was friendly. Learn from YOUR mistakes. You cannot expect players to be so conveniently clueless, that they will have such a blank slate attitude towards a foe they should know is as dangerous as a Mummy.

You can try to introduce another Mummy later, then accept that the onus is on you to convince the players. So have the PCs be somehow helpless (paralysed/bound whatever) and have this Mummy edge closer approach with none of the PCs able to do a thing to stop it. Only to have their expectations inverted where the Mummy decides to skip a perfect opportunity to coup de grace them and instead go out of their way to save them.

There are two kinds of folks that generally argue rules, and I handle them differently.

Knowledgeable players legitimately objecting to my error.

The first kind know the rules as well as you do (or better) and have a legitimate beef with how things are going down. I'll keep the action going for the other players while he argues with me, but if he cannot succinctly cite the exact rule and reference, and has to look it up, the standing ruling is that his character has been distracted. Knowing this prevents frivolous objections, and keeping the action going makes sure I'm not letting one player derail the game for all the others.

However, if he finds the rule and I am actually wrong on a judgement I have made, I will rewind events. We all role-play that the rewound events were a portend — a vision of possible events of the future granted by the gods — and I correct the situation.

These players I have no problem with, and that's how I work with them while being as fair to the rest of the group as possible.

Munchkins who just want a selfish advantage

More often than not, however, it's not a legitimate objection, it's someone seeking to override my authority with a higher authority — the game manuals — as part of a scheme to “win.”

These players I punish, by putting their fate in their own hands.

If I have a munchkin like this on my hands who's going to lock horns with me to try to "win" the game, I will ask the other players what their opinions are of his meta-gaming and how they feel I should swing my decision. If they side with him, for the rest of the adventure I agree with any “rules lawyering” he does that the party agrees with, and I meticulously write down his interpretation of the rules each time.

Then, for the next adventure module, I use todos those rules against them! After all: what the player characters can do, the NPCs can do.

Inevitably the rules lawyer will argue that I'm being unfair. The moment he goes back to argue those same rules he chose and I am now killing them all with, I point out to him (and to the rest of the group) that this was the agreed-upon interpretation of the rules, and that if you can use those rules to create what I argued was an unbalanced situation before, then the NPCs can use those muito igual rules to put them at an unfair disadvantage.

In other words, munchkins can choose their own poison. (If they don't like the taste, they shouldn't try to make me drink it either.)

It is most often at that point that the party gets a choice. They are now facing rules that are less fair than the ones I argued for originally, and they can keep them or go back to how things were. In-game another omen from the gods presents them this choice.

Then I give them cinco minutes to decide, and I watch what happens. More often than not they pull their support from the Rules Lawyer that got them into the mess, and they voluntarily keep him in check for a good portion of the campaign, if not the rest of it.

In the end, letting a selfish Rules Lawyer see what it feels like to be on the wrong end of their selfish interpretations of the rules is very effective at correcting the problem.

Rules in D&D (last time I played) were of the "maybe you want to use it, maybe you don't, but here it is" fashion.

IE: if you really want to be anal-retentive, then D&D can be as rules-intesive and game-slowing as a session of RoleMaster. But, if you want to play loose and fast, then you just take the most barebones rules and go with it.

Nobody can be expected to know all of the rules and errata that overrides them in every version or supplement that comes out.

I was typically a fast-n-loose DM. The way I handled things was via decision-tree:

1) We play

2a) if a rule comes into question, and I know it, I decide to either use the rule or override it.. but I tend to err on the side of the players. (eg:

(player) "isn't there a rule that when swallowed you have to make a saving through vs. death or immediately die?"

(me) "yes, there is.. and we're ignoring that right now, b/c that would suck."

2b) If I don't know the rule, but a player does ....

3a) if they know it from heart, and it sounds legit and reasonable, I once again make a GM judgement to either go with it or not. (ie: just b/c a player remembers a rule doesn't mean I will use it.)

3b) the moment anyone has to crack open a rule book to look up a rule, we backburner the matter, b/c we don't want to waste time looking up rules, we want to play.

This ticked off a rules-lawyer player we had a first couple of times, but the player started to realize that while I was preventing them from wasting time to look up rules they were trying to take advantage of... I was ALSO not using rules that would have royally screwed over someone. Once they realized I was trying to be fair, trying to focus more on ROLE-playing instead of ROLL-playing, and that I felt it was my job to provide an enjoyable experience for everyone (which can quickly get killed when looking up rules) they settled down and just enjoyed themselves.

That's not to say that we don't discuss the rule AFTER play. As others have said, table it for the time being, then folks can look it up afterwards.

Using this method, there was only one single time where someone found a rule after-the-fact that made me go "yeah, that rule really would have been useful", and I specifically did a rewind of game play back to when that rule would have applied and started game play from there. It was a critical rule that I did not know about, and others were hazy on, and didn't seem like that big of a deal. But, after reviewing the rule after game, we realized it could potentially make a big difference.

I was the type of GM that let players manage their own character sheets, make their own rolls, and didn't hide my rolls either. A GM can hide their rolls and flub if they want to, but I wanted to let the players know that, while I wasn't using every single rule available, and while I played loose-and-fast, I was being legit in rolling. And, them managing their own character sheets meant they could write notes for rules on how to use a skill or what-not.

But, the overall "rule" we had for gameplay was "have fun". Looking up rules killed the fun, so I pushed all of that aside. The rules lawyer got good at memorizing rules, and I relied on them for some rulings. They weren't a blatant munchkin, though.