I have this one player who's an Elven Monk who rolled 3 6 sixes in creation and thus has a +5 in dex from level 1 this makes him really overpowered in combat for example if he does the customary two unarmed strikes of monks with his mods he'll on average deal 14 damage and hit on average everything under AC 16 and he's level 2 it's kinda unbalancing the game since he can quick strike my enemies and the rest of the PCs are kinda underpowered compared to him let's take the sorcerers they can both cast magic missile if they shot Magic Missile at a foe dealing average 15 (If you add mod to each dart) that 1 spell slot used for an extra 1 damage that's pretty OP What can I do to make him a little less powerful without taking away player agency

That's always the risk with rolling. If you've only just started, perhaps allow all the other players the option to use the monk's spread instead and beef up your encounters accordingly?

Just let it go it happens, and he might find that his character is boring. 

Got a similar situation with an elven rogue; but it doesn't seem problematic.  But yeah, DM's job is to know the party and their capabilities and tailor accordingly for best play.  So this rogue is a bit of a murder machine in a fight.  The rest of the party are in a lot of situations reluctant to resort to violence ... but like having her in their (dark) corner if say persuasion on negotiation reaches an impasse.  

Also, exceptional traits, leads to exceptional feats, which leads to fame/infamy/rivalry (unless the characters are adventuring in true wilderness, but the my guess is something intelligent in whatever environment would be interested in adapting to this new threat to its ecology).  Perhaps a rival martial arts school is aware of the phenom in your party so its members start allying with the adventures antagonist, or adversaries force fights on the characters specifically to draw out the exceptionally traited one.  Does require deft handling because you don't want the game to be all about the one character, kinda like people playing Star Wars games with a Jedi in the party.  

weeeeelll. you could add in some creatures resistant to nonmagical damage. or resistant to bludgeoning damage. or have a poisonous hide and when you punch them they take damage. trouble is your PC will feel like you are out to get them. honestly in a few levels it should even out. monks can't take any of the amazing feats, so he will end up just increasing wisdom. should be fairly simple to balance 

The thing is... a 20 in your prime stat looks like a huge game-breaker at level 1. But by level 4, everyone else will be up to an 18 or 19 (probably), and suddenly the monk is only +1 better than they are. By level 8, lots of other characters (maybe everyone) will have a 20 in something, maybe an 18/19 in something else. Also, spellcasters will start getting spells like Hold Monster and Fireball and things will even out.

So... he will be uber for a level or 2. I would just roll with it. In a few levels it will even out. You could help this out by giving some nice lower tier magic items that are especially for everyone else. E.g., you could give the ranger a +1 bow... or the fighter a +1 shield. Etc.

Having played a monk before, he’s something of a glass cannon. While he’s able to dish out damage, he’s also going to take a lot of damage unless he uses his Ki points to disengage or dodge as a bonus action. And if he does that he won’t be using his bonus action for an additional unarmed strike. I wouldn’t stress over him too much. 

Just create your encounters accordingly and over time you just balance your party so that they all have equal utility (not necessarily dmg).

Like other people have said, it's not going to matter that much in a few levels. Also, remember that the monsters/enemies don't have to act like morons. If they notice that the unarmed elf is a vicious fighter in hand to hand, have them retreat and attack with ranged weapons, magic and traps*. Monks also are rather limited to when it comes to what magic items are really beneficial for them. Magic Missiles is the bane of Monks, by the way. 

*Basically use the Tucker's Kobolds principle. https://1d4chan.org/wiki/Tucker%27s_Kobolds Even weak foes can be dangerous if they use tactics and what little intelligence they have.

The odds of a player getting an 18 for a stat is about 10% when you do the 4d6 - lowest method.  Shouldn't be a surprise that one of your players had an 18.  

The easiest option is throw a magic item or two at your weaker players until the stats all even out after a few levels.  In the mean time, just throw slightly harder encounters to balance it out.

Next time I'd suggest you use point buy or have everyone roll and pick a spread that everyone uses. Player imbalance doesn't add anything to the game, is likely to upset the unlucky folks, and ends up with you doing more work as the DM trying to give weaker guys moments where they feel relevant next to their godlike buddy.

It's.not.that.big.of.a.deal.

Just.play.and.have.fun.

Focus.on.combats.where.straight.damage.isn't.the.optimal.way.to.defeat.an.encounter.

Quote from scatterbraind >>

Next time I'd suggest you use point buy or have everyone roll and pick a spread that everyone uses. Player imbalance doesn't add anything to the game, is likely to upset the unlucky folks, and ends up with you doing more work as the DM trying to give weaker guys moments where they feel relevant next to their godlike buddy.

This is the exact reason the Dungeon Dudes gave for their "better stat array" system (it's basically just a slightly beefed up version of the standard array, capping at 17 instead of 15).

I don't really understand why it's a big deal. It's a 2 point difference. Nothing massive. This is the risk you take when you roll stats. But anyway, just have an enemy cast Magic Missile or spells/features that would target their other stats like Strength, Wisdom, etc. Their Dex won't help them solve a puzzle in a room filling with water. It won't help them clear the heavy rubble out of the way to escape a tunnel that collapsed, it won't help them hold their breath long enough to get through an area filled with poisonous gas, it won't help them break out of Maximilian’s Earthen Grasp spell, or help them track a target through the wilderness.

Remember that you're a DM. Encounter difficulty is decided by you, not player stats. You are not restricted to the monster stat blocks - you are encouraged to edit and change them to suit your purpose. You can challenge players in ways outside of combat.

Quote from doctormackerel >>

That's always the risk with rolling. If you've only just started, perhaps allow all the other players the option to use the monk's spread instead and beef up your encounters accordingly?

 In my opinion, this. Everyone saying it's  no big deal, it actually is. Almost no one wants to play a character that isn't in the ballpark when it comes to being competitive, it just defies human nature. The first game I played in had 3 rolled characters while the later joining characters were point buy creations, it was awfully lopsided. Our DM allowed the point buy characters to add points up and it was way better for all players and for the DM to balance encounters. Everyone started with almost demigod stats that I found a little ridiculous personally but, I suppose that it really depends on the power level scale the DM wants to work with.

That's why I like Standard Array. Everybody has the exact same numbers. If you do point buy with new players they might now know the +/- adjustment chart, and how to game it.

Quote from Wtfdndad >>

Quote from doctormackerel >>

That's always the risk with rolling. If you've only just started, perhaps allow all the other players the option to use the monk's spread instead and beef up your encounters accordingly?

 In my opinion, this. Everyone saying it's  no big deal, it actually is. Almost no one wants to play a character that isn't in the ballpark when it comes to being competitive, it just defies human nature. The first game I played in had 3 rolled characters while the later joining characters were point buy creations, it was awfully lopsided. Our DM allowed the point buy characters to add points up and it was way better for all players and for the DM to balance encounters. Everyone started with almost demigod stats that I found a little ridiculous personally but, I suppose that it really depends on the power level scale the DM wants to work with.

I think it comes down to play style.  You bring up competitive, I know there's some power gaming where there's competition and everyone is about maxing stats.  And if the goal is some sort of race to who can be "best" I suppose fair play would mean everyone should start with some common pool, and there's a whole generation of point based RPG character constructions which the standard array method speaks to.  

That said, a lot of groups are more titled toward the collaborative role playing sides of things, and playing a character you're "dealt".  My group's party has a player with a cleric whose Constitution leads to a -2.  A massive battle liability, but this weakened, often sickly character's divinely inspired mission to corral stronger and more violent characters to the protection of others is playing out pretty well.  

There's a balance of wish fulfillment and exploration of the possible with what you're dealt.  I guess starting at a disadvantage could be problematic in some styles of play; but for others, as written here, not a big deal.  What you're given vs. what you make of it, or rather what you're given and what you make of it.

This is why I am glad my group doesn't roll stats anymore.

Quote from Wysperra >>

That's why I like Standard Array. Everybody has the exact same numbers. If you do point buy with new players they might now know the +/- adjustment chart, and how to game it.

Except that this is unbalanced towards certain classes. Some MAD classes more or less rely on you rolling well. :/

Quote from Lostwhilefishing >>

Quote from Wysperra >>

That's why I like Standard Array. Everybody has the exact same numbers. If you do point buy with new players they might now know the +/- adjustment chart, and how to game it.

Except that this is unbalanced towards certain classes. Some MAD classes more or less rely on you rolling well. :/

 all classes are balanced around standard or point buy. no class relies on rolling well, and if they did they would be terrible (you have an equal chance to roll badly)

this is coming from a person who only plays gishes (spellswords) who are nearly always MAD, and Standard array works fine. take blade singer (imo the most MAD single class)

high elf with standard: str: 8, dex: 14 (16 with racials), Con 13, wis: 12, int: 15 (16 with racials) char: 10.

or Paladin. Half elf with standard: str: 15(16 with racials), dex 8, con 13(14 with racials), wis 12, int 10, char 14(16 with racials)

if you mean niche multi class builds (druid/paladin/rogue) then yea you are gonna need to roll well. but for singleton's classes standard array and point buy are balanced