The set up goes thusly, I am a new-ish DM and one of my players wants to a character that punches like a jackhammer. I'm on board with this because, well, it's cool. I even helped him to homebrew a set of Knuckledusters that count both as "Light" weapons and count as unarmed strikes. The problem we have run into is exactly how many punches can one character throw?

The applicable factors are as follows:

-Frenzy Barbarian's Extra Attack

-The Monk's Flurry of Blows and Martial Arts

-The Fighter's Action Surge and Extra Attack Feature

-The Knuckledusters of Muta-Oda, Light and Attacks with these weapons count as Unarmed Strikes

I've run the numbers in a few different orders and the result general is the the mid-30s. If there is anyone out there who knows the DnD version of the "Order of Operations" I would be most grateful for your input.

              -Yours, Beaumont Westman

Assuming Monk lvl 5, Fighte lvl 1 and tapping ki for flurry of blows every round for the following:

Action: Attack (2 punches)

Bonus action: Flurry of Blows (2 more punches)

If you add in feats you could squeeze in one more attack using a reaction with something like Sentinal.

If you have a haste spell active then you can get 1 mroe attack per round.

Action Surge to repeat Above for potentially 9 attacks in one round (you dont get a 2nd bonus action or reaction form either Action Surge or Haste)

So all of that means for one glorious round you get upto 9 attacks if you can use your action, bonus action, haste action, reaction and Action Surge, then you are down to 6 attacks per round, still none to shabby for a level 6 character. Just bear in mind it'll also cost you 1 ki point per round to use flurry of blows otherwise your are down to 8 then 5 attacks per round.

So if that is correct (and if it isn't someone please correct me) thats 33 attacks over 5 rounds of comabt but leaves you out of ki.

I left Barbaroian out of the mix as the Frenzy attack and flurry of blows both use a bonus action so you can only do one or the other not both in a round of combat.

You can only benefit from extra attack once, meaning if you get the feature from both fighter and monk, only 1 applies.  Also, frenzy from the barbarian uses a bonus action as does flurry of blows, so you could only use 1 of them, and flurry of blows gives you 2 unarmed attacks as opposed to the barbarian's 1.

Yeah, most of these things don't stack. Your best bet is to go monk with 2 levels in fighter for action surge as Rob outlined above (except he mistakenly put that Fighter gets Action Surge at 1 when it is actually level 2). Outside of your Action Surge round, that will be doing 4 attacks (2 with Extra Attacks, 2 with Flurry bonus action) until you run out of ki, then 3 attacks indefinitely. At high levels, a Fighter could squeeze out a little more since they get up to 4 attacks with the Attack action and then can make a bonus attack with Polearm Mastery or Two Weapon Fighting or whatever else you can find. But yeah 30 is not gonna happen.

But keep in mind that the description of Attack is totally up to you aside from the range and type of damage dealt. If you want to describe one attack as a flurry of 10 punches there is nothing stopping you.