I'd like some feedback on the math for Nick/Hunter's Mark. (The missus is building a dagger monk)
Since you have to give up the monk's Flurry of Blows to cast HM/Hex in the first place, that would impact your average damage over two or more rounds, correct? And the risk of losing the spell due to concentration affects that as well?
Basically, I've seen other comments online that suggest the combo doesn't work well in practice.
I don't have the math, but I can tell you some actual experience in general and from experience.
In general, always pay attention to the action economy. Specifically, the one thing that messes up the most people is the "Bonus Action." You get one bonus action. Period. No more. Some have specific triggers and timings- if they don't, you get to choose when to use it. But you only ever get one in a round. So if you have a bunch of cool things that require the use of a bonus action, you will always be choosing what to use. In other words- don't load up on abilities that require the bonus action.
With that in mind-
If you have ranger/monk to get weapon mastery and you are using nick mastery with two daggers (has to be two light weapons), then:
Nick moves the bonus action from TWF to the action. That means that you get two dagger attacks as MONK WEAPONS with the attack action.
You now have a bonus action.
As a ranger, you can use the bonus action to cast hunter's mark at the beginning of combat. That lasts for a while, so from the second round on (or earlier, if you cast it before combat starts) your bonus action is free to use flurry of blows or a bonus unarmed strike.
HM is concentration, so if you're hit, you have to make a save (constitution) to keep it up.
In addition, when the target dies, you will need to use the next round's bonus action to re-target the HM.
(All this applies to hex, but Warlock doesn't give you Weapon Mastery)
As a general rule, you'll be spending the first round of combat activating HM to get the extra damage. If you're fighting a lot of squishy critters that die quickly, you might end up not getting to use your bonus action for an unarmed attack or flurry of blows because you're constantly re-targeting. OTOH, if you're fighting a massive bag of hit points, you're going to be doing a lot of damage from the HM- not just the first round, but especially from the second round on when you can apply it to the flurry of blows.