Legal use of True Strike/Sneak Attack?

[Kastor]

I have an idea for a duelist rogue, meant for 1v1 situations.
It would be a rogue of at least 4th level (3 if arcane trickster) with two weapon fighting, a dagger in their main hand, and a rapier in the right. Their gimmick would be attacking with their bonus action, then using their action to cast True Strike- thus granting the next strike advantage and qualifying it for Sneak Attack. Rinse and repeat.

Would this work in RAW? This is obviously far from an optimized build, but I would enjoy it for flavour.

[PhantomSoul]

If I'm understanding right, every turn you intend to use your bonus action to make an (offhand?) attack while using the cast a spell action to cast true strike (preparing for the following turn).

Maybe I'm missing information you have in mind, but if it's meant to be an offhand attack from dual wielding, I don't see how you're getting those attacks. At higher levels Haste would work or eldritch knight levels give that ability, but I don't know which feature lets you get the bonus action attack (since offhand attacks require the attack action).

[Aett_Thorn]

In order to make an off-hand attack with two-weapon fighting, you need to use your action to Attack. So you can’t just make a Bonus Action attack without also making an Action attack.

[Tanarii]

TWF also doesn't work with the rapier/dagger combo without a feat.

[JNAProductions]

Yeah, not seeing how you’re getting a BA attack. Can you explain further?

[Mastikator]

That's not legal.
https://roll20.net/compendium/dnd5e/Combat#toc_41

[Zhorn]

Like said above; the 'when you take the Attack Action' prerequisite is going to brick wall you on that plan.

Now while I do not recommend you actually do this; there is a way to flip that order on Action and Bonus Action.
A 3 level dip into Sorcerer to pick up the Quickened Spell Meta Magic ability so you can quicken True Strike to a Bonus Action after you have attacked with your Attack Action each round, prepping the True Strike for the following round.
It's a waste of sorcery points and class levels, and delay your Rogue progression, but it would work.

[Kastor]

In order to make an off-hand attack with two-weapon fighting, you need to use your action to Attack. So you can’t just make a Bonus Action attack without also making an Action attack.

Aha! That's exactly the foil I was afraid of- thank you so much for highlighting it.

[Kastor]

Like said above; the 'when you take the Attack Action' prerequisite is going to brick wall you on that plan.

Now while I do not recommend you actually do this; there is a way to flip that order on Action and Bonus Action.
A 3 level dip into Sorcerer to pick up the Quickened Spell Meta Magic ability so you can quicken True Strike to a Bonus Action after you have attacked with your Attack Action each round, prepping the True Strike for the following round.
It's a waste of sorcery points and class levels, and delay your Rogue progression, but it would work.

I had considered this, but it felt too convoluted. Dropping a feat is one thing, but this is meant to be a low-level gimmick, and there's few levels enough.
Thank you for your input!

[MaxWilson]

I had considered this, but it felt too convoluted. Dropping a feat is one thing, but this is meant to be a low-level gimmick, and there's few levels enough.
Thank you for your input!

Consider Shield Master instead to shove prone with your bonus action. Check first with your DM to see whether they read it as requiring you to Attack then bonus Shove (won't work for you), or if bonus Shove then Attack is legal.

FWIW as DM I read it as not caring about the order because unlike Flurry of Blows it doesn't say "immediately after", just "if." Ask your DM though.

Also note that if you move away from a prone enemy their opportunity attack has disadvantage, and they have to spend half their movement standing up, so if you move 20' or so they won't usually be able to attack you regularly--one opportunity attack at disadvantage is all they get. This is especially significant against monsters like Orogs who normally get two or more attacks.

Or, if your DM says no, then just take Skulker and gain advantage through being hidden. Use ranged weapons.

[RSP]

Consider Shield Master instead to shove prone with your bonus action. Check first with your DM to see whether they read it as requiring you to Attack then bonus Shove (won't work for you), or if bonus Shove then Attack is legal.

FWIW as DM I read it as not caring about the order because unlike Flurry of Blows it doesn't say "immediately after", just "if." Ask your DM though.

Also note that if you move away from a prone enemy their opportunity attack has disadvantage, and they have to spend half their movement standing up, so if you move 20' or so they won't usually be able to attack you regularly--one opportunity attack at disadvantage is all they get. This is especially significant against monsters like Orogs who normally get two or more attacks.

Or, if your DM says no, then just take Skulker and gain advantage through being hidden. Use ranged weapons.

Though, keep in mind Rogues don’t have access to shield prof, so this would need something more to be a regular Rogue trick.

[Hairfish]

Have you seen the Swashbuckler archetype? It's a duelist rogue meant for 1v1 situations. And attacking twice is mechanically superior to attacking once with advantage, except for a few edge cases.

[animewatcha]

What about arcane trickster with the spells being focused around granting advantage in different circumstances? Like ranged trips, grapples, etc.

[Greywander]

Have you seen the Swashbuckler archetype? It's a duelist rogue meant for 1v1 situations. And attacking twice is mechanically superior to attacking once with advantage, except for a few edge cases.
I think the purpose of advantage is to make the attack qualify for Sneak Attack, since you have no allies to be next to your opponent. Now, there are several rogue subclasses, including the Arcane Trickster, who have ways of making Sneak Attacks without having an ally next to their opponent and without needing to hide every round.

What I would consider in this situation is picking up Athletics expertise and not dumping STR. Grapple, shove prone, then stab stab stab. This has the advantage of giving your opponent disadvantage on their attacks, however because rogues don't get Extra Attack you'd need to spend two turns setting it up, so YMMV if it's worth it. Picking up Extra Attack from another class makes this much more viable, but it does delay your rogue progression and therefore your Sneak Attack damage.

Another alternative is to dip into fighter for the Blind Fighting style, dip into wizard or sorcerer for Fog Cloud, and then enjoy what is essentially Greater Invisibility for the rest of the fight. Magic Initiate for Fog Cloud works, too. The downside is that nobody gets to see how cool you are, if that's something you care about.

[IsaacsAlterEgo]

I have an idea for a duelist rogue, meant for 1v1 situations.
It would be a rogue of at least 4th level (3 if arcane trickster) with two weapon fighting, a dagger in their main hand, and a rapier in the right. Their gimmick would be attacking with their bonus action, then using their action to cast True Strike- thus granting the next strike advantage and qualifying it for Sneak Attack. Rinse and repeat.

Would this work in RAW? This is obviously far from an optimized build, but I would enjoy it for flavour.

This doesn't work as discussed previously, but if you want an alternative that works just as well, you can use the Steady Aim class feature from Tasha's Cauldron of Everything that lets you use your bonus action to grant yourself advantage, so that you can make an attack with your Action at advantage.

It's basically the same sort of set up you're looking for, just with the action usage swapped and you aren't using a spell to do it, but you could flavor it as using a faster, more efficient version of True Strike that your character came up with on their own or something like that!