While monks have access to some strong control options, most notably stunning strike, they tend to suffer in the DPR department, especially at higher levels. The martial arts weapon damage dice scales slowly, and monks have few good options for increasing their damage. This is a build that attempts to work around that. Using the second level Sorcerer spell Shadow Blade, we can create a weapon that deals 2d8 psychic damage on a hit, and, crucially, is a simple weapon, which means it also counts as a monk weapon. RAW, a Kensei monk can choose the shadow blade as one of their Kensei weapons as well, which opens up some specific tricks, like using Sharpen the Blade to make the shadow blade a +3 weapon. This is my attempt at a build based on using Shadow Blade on a monk.
Race: Wood Elf
This will be an Elven Accuracy build, and that limits us to the elf subraces. Since we're going to be using exclusively sorcerer powers that don't require a check, we're free to take a Charisma of 13, which allows us to get 17 Dex and 16 Wis at level 1. 12 Con is the best we can afford, and Str and Int are dumped.
Ability scores: (generated using point buy)
8 Str, 15+2 Dex, 12 Con, 8 Int, 15+1 Wis, 13 Cha
Dexterity is our attacking stat, and a postracial 17 is taken to take advantage of the +1 given by Elven Accuracy. Our AC and our Ki DC are tied to wisdom, so we need that high as well. 13 Charisma is needed to multiclass into Sorcerer, and since we won't be using any spells that require a check, we can leave it there. 12 Con is unfortunately the best we can afford.
Level 1: Sorcerer 1
This is a melee build with low Con that plans to concentrate on spells, so it is absolutely necessary for us to have Constitution save proficiency. Because of that, we're taking sorcerer first. We're not going far enough into Sorcerer to gain the level 6 benefit of our bloodline for a long time, which means our choice is mostly based on which level 1 feature we prefer. I recommend Divine Soul, which gives us Favoured by the gods, as well as access to Cleric spells.
Starting equipment: Light crossbow and 20 bolts, Arcane Focus, Explorer's pack
We're not a monk yet, and we need something to do when we run out of spell slots, so a light crossbow works well with our 16 Dex.
Cantrips: Booming Blade, Guidance, Minor Illusion, Prestidigitation
Booming Blade gives us a weapon attack to use with Quicken Spell later, as well as at level 5 when we don't yet have Extra Attack. Since we don't have an attack-caliber Charisma, the rest of our cantrips are utility options.
Spells: Shield, Sleep.
At this level, we play the same as every other sorcerer: We cast Sleep during a big fight, and otherwise use our hand crossbow to attack. Thankfully, Sleep doesn't care about your ability score, so it doesn't matter that we don't have a +3. We don't have mage armor, because it becomes obsolete next level and we won't be able to retrain it out, so try to save a spell slot for shield, and also try to stay out of the enemy's way.
Level 2: Sorcerer 1/Monk 1
With our 1 level in Sorcerer taken, we're now going to rush to monk 5 to get Extra Attack and Stunning Strike. Our first level in Monk brings our armor class from 13 to 16, and also gives us an extra 1d4 punch every round as a bonus action. As before, we have sleep for the harder fights and Shield in case we get hit. Note that unfortunately, casting Booming Blade does not allow us to follow up with a martial arts attack, since you're not taking the attack action.
Level 4: Sorcerer 1/Monk 3
The monastic tradition we're taking is Kensei, and our first two Kensei weapons will be Longsword and Longbow. These are the most damaging weapons we have access to, and will outperform our martial arts attacks for a while.
Level 5: Sorcerer 1/Monk 4
We get our first ASI at this level, and we're taking Elven Accuracy with +1 Dex, bringing our Dex to 18 and giving us a nice bonus should we happen to be attacking with advantage. This is also the level where Booming Blade scales, and you can use it to help discourage enemies from chasing you. Hit them with a booming blade, then use Step of the Wind to disengage.
Level 8: Sorcerer 3/Monk 5
After getting our fifth level in Monk, we're going to go up to 3 levels in Sorcerer to gain access to Shadow Blade. This spell, which only takes a bonus action to cast, gives us access to the most powerful monk weapon in the game, 2d8 base damage at this level, scales when upcast. We also get Metamagic at this level, which lets us, on subsequent turns, attack twice with the shadow blade and then quicken a booming blade, for a total of 7d8 + 12 damage if all three hits land, plus 2d8 more if they move. We won't have the sorcery points to do this consistently, but it's nice to have when we need it.
Level 10: Sorcerer 4/Monk 6
After we get Shadow Blade, we take one more level of Monk, which gives us another choice of Kensei Weapon (we're choosing the shadow blade). We also get deft strike, but spending a ki point on 1d6 damage isn't that useful unless it's on a crit. We then take a fourth level in Sorcerer for the ASI and bring our Dex to 20.
Level 13: Sorcerer 5/Monk 8
We take a fifth level in Sorcerer to access 3rd level slots. A shadow blade upcast to level 3 gives you a weapon that deals 3d8 damage per hit. On the Monk side, we get Evasion, which will help with our weak Dex save, and we get a third ASI, which we put into Wisdom.
Level 17: Sorcerer 5/Monk 12
We're going up to 12 levels in Monk for the level 11 Kensei ability Sharpen the Blade, plus an extra ASI. Sharpen the Blade is the only way to grant a magic weapon bonus to the shadow blade, which means with the use of two bonus action, a level 3 slot, and 3 Ki, we're creating a +3 weapon that deals 3d8+8 damage per hit. We also get another ASI, which we're putting into our Wis to get that to 20.
Level 20: Sorcerer 8/Monk 12
We take our last three levels in Sorcerer for the final ASI (we're taking War Caster) and more sorcery points for Quicken Spell.
It takes two rounds of bonus actions to set up, but once we have everything ready, we're attacking twice with a +14 bonus to hit for 3d8+8 damage per hit using our attack action, then using a quickened booming blade for another 6d8+8. On any of our hits, we can apply stunning strike to force our target to make a DC 18 Con save or be stunned, after which we have advantage and 3 attack rolls from elven accuracy. We can also spend one ki point to use Deft Strike and add an extra 1d8.
Race: Wood Elf
This will be an Elven Accuracy build, and that limits us to the elf subraces. Since we're going to be using exclusively sorcerer powers that don't require a check, we're free to take a Charisma of 13, which allows us to get 17 Dex and 16 Wis at level 1. 12 Con is the best we can afford, and Str and Int are dumped.
Ability scores: (generated using point buy)
8 Str, 15+2 Dex, 12 Con, 8 Int, 15+1 Wis, 13 Cha
Dexterity is our attacking stat, and a postracial 17 is taken to take advantage of the +1 given by Elven Accuracy. Our AC and our Ki DC are tied to wisdom, so we need that high as well. 13 Charisma is needed to multiclass into Sorcerer, and since we won't be using any spells that require a check, we can leave it there. 12 Con is unfortunately the best we can afford.
Level 1: Sorcerer 1
This is a melee build with low Con that plans to concentrate on spells, so it is absolutely necessary for us to have Constitution save proficiency. Because of that, we're taking sorcerer first. We're not going far enough into Sorcerer to gain the level 6 benefit of our bloodline for a long time, which means our choice is mostly based on which level 1 feature we prefer. I recommend Divine Soul, which gives us Favoured by the gods, as well as access to Cleric spells.
Starting equipment: Light crossbow and 20 bolts, Arcane Focus, Explorer's pack
We're not a monk yet, and we need something to do when we run out of spell slots, so a light crossbow works well with our 16 Dex.
Cantrips: Booming Blade, Guidance, Minor Illusion, Prestidigitation
Booming Blade gives us a weapon attack to use with Quicken Spell later, as well as at level 5 when we don't yet have Extra Attack. Since we don't have an attack-caliber Charisma, the rest of our cantrips are utility options.
Spells: Shield, Sleep.
At this level, we play the same as every other sorcerer: We cast Sleep during a big fight, and otherwise use our hand crossbow to attack. Thankfully, Sleep doesn't care about your ability score, so it doesn't matter that we don't have a +3. We don't have mage armor, because it becomes obsolete next level and we won't be able to retrain it out, so try to save a spell slot for shield, and also try to stay out of the enemy's way.
Level 2: Sorcerer 1/Monk 1
With our 1 level in Sorcerer taken, we're now going to rush to monk 5 to get Extra Attack and Stunning Strike. Our first level in Monk brings our armor class from 13 to 16, and also gives us an extra 1d4 punch every round as a bonus action. As before, we have sleep for the harder fights and Shield in case we get hit. Note that unfortunately, casting Booming Blade does not allow us to follow up with a martial arts attack, since you're not taking the attack action.
Level 4: Sorcerer 1/Monk 3
The monastic tradition we're taking is Kensei, and our first two Kensei weapons will be Longsword and Longbow. These are the most damaging weapons we have access to, and will outperform our martial arts attacks for a while.
Level 5: Sorcerer 1/Monk 4
We get our first ASI at this level, and we're taking Elven Accuracy with +1 Dex, bringing our Dex to 18 and giving us a nice bonus should we happen to be attacking with advantage. This is also the level where Booming Blade scales, and you can use it to help discourage enemies from chasing you. Hit them with a booming blade, then use Step of the Wind to disengage.
Level 8: Sorcerer 3/Monk 5
After getting our fifth level in Monk, we're going to go up to 3 levels in Sorcerer to gain access to Shadow Blade. This spell, which only takes a bonus action to cast, gives us access to the most powerful monk weapon in the game, 2d8 base damage at this level, scales when upcast. We also get Metamagic at this level, which lets us, on subsequent turns, attack twice with the shadow blade and then quicken a booming blade, for a total of 7d8 + 12 damage if all three hits land, plus 2d8 more if they move. We won't have the sorcery points to do this consistently, but it's nice to have when we need it.
Level 10: Sorcerer 4/Monk 6
After we get Shadow Blade, we take one more level of Monk, which gives us another choice of Kensei Weapon (we're choosing the shadow blade). We also get deft strike, but spending a ki point on 1d6 damage isn't that useful unless it's on a crit. We then take a fourth level in Sorcerer for the ASI and bring our Dex to 20.
Level 13: Sorcerer 5/Monk 8
We take a fifth level in Sorcerer to access 3rd level slots. A shadow blade upcast to level 3 gives you a weapon that deals 3d8 damage per hit. On the Monk side, we get Evasion, which will help with our weak Dex save, and we get a third ASI, which we put into Wisdom.
Level 17: Sorcerer 5/Monk 12
We're going up to 12 levels in Monk for the level 11 Kensei ability Sharpen the Blade, plus an extra ASI. Sharpen the Blade is the only way to grant a magic weapon bonus to the shadow blade, which means with the use of two bonus action, a level 3 slot, and 3 Ki, we're creating a +3 weapon that deals 3d8+8 damage per hit. We also get another ASI, which we're putting into our Wis to get that to 20.
Level 20: Sorcerer 8/Monk 12
We take our last three levels in Sorcerer for the final ASI (we're taking War Caster) and more sorcery points for Quicken Spell.
It takes two rounds of bonus actions to set up, but once we have everything ready, we're attacking twice with a +14 bonus to hit for 3d8+8 damage per hit using our attack action, then using a quickened booming blade for another 6d8+8. On any of our hits, we can apply stunning strike to force our target to make a DC 18 Con save or be stunned, after which we have advantage and 3 attack rolls from elven accuracy. We can also spend one ki point to use Deft Strike and add an extra 1d8.
