How can unarmed strike be made to work with a rogue's sneak attack?

Question

The question Can unarmed strike work with a rogue's sneak attack? explores whether a multi-classed monk/rogue's sneak attack and unarmed strike can be used together.

I want to explore a variation on that question: is there any way in the official rules to grant finesse to the monk's unarmed attack so that it can work with Sneak Attack? Perhaps with some sort of finessed glove or boot, such as if the monk/rogue had been wearing a spiked glove perhaps?

(ps I'm a new DM with only about 20 hours / 4 sessions under my belt)

The text relating to Martial Arts unarmed strikes states (PHB pg 78):

You gain the following benefits while you are unarmed or wielding only monk weapons and you aren't wearing armor or wielding a shield...

Answer 1

There is no RAW way to combine Sneak Attack with Unarmed Strikes

In order to allow this, you'd need to either waive the Sneak Attack requirement for a Finesse weapon, or create a homebrew item that work as a finesse weapon but still an unarmed strike.

Even Unearthed Arcana has the major warning that it is not tuned for multiclassing, but once you start multiclassing with UA or Homebrew, you enter unprepared territory. It's up to the DM and they're table to decide how they want things to work. Allowing certain interactions (i.e. if the spiked glove is considered a finesse weapon), may break certain other things (i.e. rogue sneak attack.) There are generally trade-offs for making decisions and if those tradeoffs disappear because of homebrew, then you may end up with a character who is more powerful than they should be.

The dangers of allowing this interaction

But in the end, it's up to the DM decide if those interactions break their game. Sneak attack was purposefully made to NOT integrate unarmed strikes. If you have a way to turn an unarmed strike into an armed strike, it may cause a problem. If you don't think it does, or you can handle it by increasing enemy difficulty, etc, then go for it.

A note on unarmed strikes(from guildsbounty and Miatog)

It is important to note that monk unarmed strikes are not necessarily nor are they always a punch. The strike can come from an elbow, knee, head, etc - which is why the Monk doesn't need a free hand to make use of their unarmed strikes.

In addition, once you add a finesse weapon to allow Sneak Attack, you are no longer making an unarmed strike. You have armed yourself with a finesse weapon.

Answer 2

There is no RAW way to combine these but...

A monk's Martial Arts feature (PHB, p. 78) says:

• You can use Dexterity instead of Strength for the (monk martial arts) attack and damage rolls of your unarmed strikes and monk weapons.

Sneak Attack (PHB. p. 96) says:

The attack must use a finesse or a ranged weapon.

And Finesse (PHB, p. 147) uses…

… your choice of your Strength or Dexterity modifier for the attack and damage rolls.

So although in the rules as written unarmed strikes aren't finesse weapons, a monk's unarmed strikes seem to have either the finesse property or something very similar.

Finally, in answer to your question, all that would be necessary for these to work is for you to say that at your table that monks' martial arts allows them to use finesse with all monk weapons and unarmed strikes.

This would put in the missing link and connect the dots for you.