Need help with theorycrafted build.

[CisoSecond]

My friend and I were talking about Haste and how fast a dashing level 20 monk would move with it when we started to theory craft a build that we think could be super fun.

The build would be 3 Rogue/X Monk and then either Ranger or Druid (Moon). We're thinking Druid for the spells and general shapeshifting, and Ranger for better scaling and more shared stats. We're not entirely sure about the exact splits. It's possibly that we might do Fighter instead of Ranger, Druid, or Monk for the Battle Master archetype for tripping, disarming, etc and action boost. (Admittedly as I'm writing this that seems like a fantastic option.)

The build's goal is to create sort of deadly blur in combat. They can move great distances and with some self-casted haste (from an item) they would be able to take a multitude of actions in combat. With haste the character should be able to do combinations of attacking, casting spells, picking locks and disabling traps (from the Thief archetype), dashing, disengaging, etc.

The snag that we're hitting is which is the best mix of classes and splits, and whether or not we're overlooking some key rules that would disable this. Will the character even be useful?

Here's hoping that someone can help us out with this, the fantasy of the build really appeals to us and if it all works out we'll be looking to run it in our upcoming game.

P.S. As a side note, the DM that is running us has decided to let us do 4d6 reroll 1s and 2s drop the lowest. Stats aren't a limit for this character.

[Shaofoo]

You seem to truly lack focus on what you really want.

First of all expecting a magic item to help you build is already a massive strike against you and one that you will not recover. Magic items are fully within the DM's right to give or not give and he has full control over what appears or doesn't appear. Also in the DMG I am not sure if there is an item that allows you to Haste, there is a potion that gives you haste but that is a very rare item. Don't know any archetype that depends on a very rare consumable to work.

Also with Haste you have two actions and a bonus action plus your movement. I don't know of any other way to increase those actions so you blur of movements is no better than any other class, you won't be unique in this regard.

Personally either go full Monk or go Monk 17/Rogue 3 and if you really want Haste instead tell your friend to go Sorcerer since they have Con saving throws and can even twin Haste and can lengthen Haste.

[MinotaurWarrior]

Honestly? Just go woodelf or birdfolk monk 20, with the mobility feat, and wear boots of speed.

Level 1-4: You're benefiting more from the high stats than anyone else, because you're the only guy adding his ability mod to a second attack. I assume you're at least going this far single-classed, because I really think both the racial mods and mobility are core to your concept.

Level 5: You either walk 55 or fly 70, are immune to AOO, can get four attacks per round (all with high ability mods) and have both stunning fist and open hand technique. You can't skip this without gimping yourself.

6-8: this is where I guess you could add another class. Monks get 5ft of movespeed, Evasion, stillness of mind (which ime is better than it looks on paper), a minor healing ability, an ASI, and 3 ki points.
Rogues get: expertise (great on a wood elf), 2d6 sneak attack, cunning action, and assassinate. Assassinate and expertise (stealth) are very powerful... but not as much for a monk chasis as for another class, because your DPR isn't based on having a bunch of damage dice, and your greatest value to the party is in creating status effects. Sneak attack and cunning action both frankly go against monk strategy. And you're losing 3 ki points per short rest (9 per day)
Fighters get: Dueling style, Second Wind, Action Surge, and four superiority dice. None of the maneuvers inflict status effects as good as stunning, but this will clearly amp up your DPR, and contributes to the role you've chosen. Second wind is just worse than monk healing at this point, but neither class cares. What you're sacrificing is a bit of survivability, speed, and an ASI. I can see why you'd choose this, but for someone who's already monk 5, there's essentially no reason to go further than BM 3, and then you've cut yourself off from the deeper monk features.
Rangers get: Dueling Style, Horde Breaker, 3 first level spells, and 3 cantrips. I haven't done the math, but I suspect this is actually usually going to be better DPR-wise than the BM, because monks are going to be really good at proccing Horde Breaker - you can open hand push enemies together, if needed. You're also likely faster than the pure monk, because of longstrider. But, again, you've lost durability and ki points, plus hunter's mark competes with monk class features.
Druid's get: Very DM-dependant benefits, because AFAIK this edition has no clearly laid out rules for how monster natural attacks work, unlike 3.X. If they're absurdly generous, and say that the melee weapon attacks listed under a monster's "Actions" heading work just like any other melee weapon attack, and count as either monk weapons or unarmed strikes then I think that Giant Goat Monks are ridiculously good. If they assume that things work similarly to 3.X, then Druids Monks just suck and have no synergy.

So, in short: with a generous DM, Druid Monks are amazing. Otherwise, Rangers and BMs are decently synergistic at level 8, but rogues really only work well if you're obsessed with getting assassinate.

Next, let's look at levels 9-11: when a Monk 5/ BM or Ranger 3 could go Monk 5/BM3/Ranger3

Monk gets: another +5 movement, an unarmed damage die increase, immunity to poison and disease, all-day sanctuary, more monk healing, and +3 ki.

So, the monk catches up to the rangermonk's movement speed, exceeds the size of the BM's bag of tricks, gains another survivability boost (albeit a very minor one), and is arguably the best vanguard any party can have. Before the first combat, enemies have to make a saving throw before they get to make attack rolls. That immensely decreases the chances of your party getting hit before you can hit back. You can also potentially do cheeky things with object interactions and the like, though that's a fringe benefit.

The BM Ranger Monk does, however, almost certainly have better DPR. They can get up to seven attacks in a round - five dealing 1d8+2+ability mod, two dealing 1d6+ability mod, plus the 4d8 superiority dice, and a spattering of hunter's mark dice. If your DM hands out magical weapons, this can be truly ridiculous. But this leads to a very different strategy than what you said you want to do. This character is happiest not when it's running around influencing the whole battle, but instead when it can wail on a guy with focus fire.

At this point, I think there's a strong case for the multiclass, but the pure monk fulfils your concept better.

In the next three levels, 11-14, the monk clearly pulls ahead, with universal proficiency and save re-rolls, and then at 17 you're ridiculous with quivering palm.

[Shaofoo]

The BM Ranger Monk does, however, almost certainly have better DPR. They can get up to seven attacks in a round - five dealing 1d8+2+ability mod, two dealing 1d6+ability mod

How can you get seven attacks a round?

Or how are you getting 5 attacks with your Attack option?

[Malifice]

Race Wood elf. Feat mobile and Alert. Have a base 45' move.

Rogue 3 (Assassin) for cunning action. Take expertise in perception and stealth. Nab assasinate.
Fighter 3 gets you action surge. Ride it out for BM manouvers
Sorcerer 5 gets you Haste and invisibility. Select quicken spell.
Druid 1 gets you longstrider.
The horribly broken playtest Ranger gets to take two actions on turn 1 of every combat, and also grants an even more broken ability at 2nd level that renders you immune from return attacks (youre perma hidden). Two levels is all you'll need.
Take 6 levels of shadow monk for the +15' speed and the ability to teleport 60' as a bonus action.

Your speed for a turn is now 60' (70' with longstrider active, 140' with haste). Your maximum move is (speed)+(action)+(action)+(bonus action)+(haste action) or 700' per round (80mph), but you can sustain speeds of 560' per round for a minute.

Your M/O is to have longstrider and haste active, then stealth up to your enemy (your combination of pass without trace, and expertise in stealth makes this a no-brainer), and then launch a devastating nova strike featuring:

Round 1 (surprise round) Attack action (ranger) make 2 attacks, attack action (standard) make 2 attacks, attack action (action surge) make 2 attacks, bonus action (flurry of blows) make 2 attacks, haste (make 1 attack). Spit your 140' base move up in there however you feel like it.

Bear in mind, all nine of these attacks are at advantage and are automatic critical hits from assasinate. If you didnt beat him on initiative, make sure you drop the rest of your Ki points on stunning attacks to ensure he cant do squat before you beat him again next turn.

If you won initiative, its now your turn again (only 5 attacks this turn). Again, stun him senseless.

If whatver youve just murdered isnt yet dead, unless he can beat a DC 30 odd perception check, he cant attack you back thanks to your broken Ranger ability to remain hidden even while beating someone silly.

Feel free to mix movement in between these attacks.

Basically you'll emerge from the darkness, racing around the battlefield as a blur, critstunning your enemies (and knocking them flat with BM manouvers). You can also do fun things like move 140' (attack 5 times with action surge and haste) bonus action dash 140' backwards.

[MinotaurWarrior]

How can you get seven attacks a round?

Or how are you getting 5 attacks with your Attack option?

Extra attack makes every attack action include two quarterstaff attacks. You action surge, to get two of those. You also use flurry of blows, to get two more fist attacks. Finally, horde breaker gives you the seventh attack.

[Shaofoo]

Extra attack makes every attack action include two quarterstaff attacks. You action surge, to get two of those. You also use flurry of blows, to get two more fist attacks. Finally, horde breaker gives you the seventh attack.

Horde Breaker forces you to make that attack to someone else and if that someone else is next to the original target.

But I don't think multiclass would work, especially the 3-5 class pile up that is being presented. Sure as a mental exercise and on paper it could work but you'll have to realize that actually getting to that spot isn't going to be in any way easy or quick. You will be losing out on ASIs and other features as you go along so you'll be weaker down the line as a result.

I still say the best way is to get your friend to be a buffing Sorcerer and you go full monk or a bit of rogue. It seems your friend is just as interested in the concept so having him actually give you the buffs will go a long way.