Multiclassing - Extra Attacks and Sneak Attacks

Question

So, I'm playing a level 5 Fighter Battle Master. I'm thinking about multiclassing with Rogue, for the Sneak Attack. I'll use a rapier, since it has 1d8 damage and acuity. At level 5/1 (Fighter/Rogue)

I want to do a combo like this (considering I hit every attack):

• Use my basic action to attack; Proc Extra Attack to do it twice; on my first hit I'll use the "Trip Attack" maneuver to add extra damage and cause a Strength saving throw

• As he fails the throw, he will fall prone; Every attack after that is with Advantage; I'll finish my first Attack action with the Extra one at advantage

• Then, I'll use "Action Surge" and gain a extra Action; Then use this action to Attack again; This time, since I have advantage on both the attacks, I'll use "Sneak Attack" to add 1d6 to each of "Extra Attack" attacks

• Dealing in total: 2d8 on the first attack (Trip Attack), 1d8 on the second, 1d8 + 1d6 on the third and forth attacks.

A total of: 5d8 + 2d6

Can this be done?

Seeing as you can use Sneak Attack once per turn to add 1d6 to the DMG roll of an attack you hit. Since my attack action allow me to attack twice, would that work?

Answer 1

Unfortunately, no, this does not work as detailed.

This answer is based in 5th edition D&D for rules and rulebook citations.

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(I think you've conflated "having multiple attacks" with "having more than one action", which are mechanically distinct. I answer as to the latter, as even a single-classed Rogue can attack twice on a turn via two-weapon fighting.)

Action Surge does not grant you another turn, it grants you a second action on the same turn:

On your turn, you can take one additional action. ^{(Player's Handbook, p. 72)}

Sneak Attack remains explicitly only once per turn:

Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. ^{(Player's Handbook, p. 94)}

Even with Action Surge, it's still the same turn. Only one Sneak Attack roll applies, no matter how many attacks you can make or actions you can take.

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I will point out, however, Sneak Attack can be applied outside of your turn on your reaction. Unless you have a feature granting you additional reactions, that means a theoretical maximum limit of twice within a single combat round in ideal conditions.