LV 6 Deathly Assasin build

[Louro]

Hello.
I'm master of a short campaign to test the 5th edition. After the first play I see I will need an assasin NPC sooner than later. My party is of 4 players of 5 level (wizard, sorcerer, cleric and monk).
I don't want the NPC to be too powerfull, but definitively a threat. So, here is the idea. In bold the most relevant points.

Rogue 3 (assasin)
- Expertise stealth
- Cunning Action
- Sneak Attack: +2d6
- Assasinate: Advantage & critical VS those who haven't taken a turn in the combat yet.

Fighter 3 (Battlemaster)
- Fighting Style: 2 weapon fighting
- Action Surge
- 3 maneuvers (4 superiority dice): +1d8

It will be something like this:
- Surprise round (Either automatically surprised or stealth roll VS Passive perception, depending on the situation)
- We roll initiatives (Nasty if the assasin gets to act first, wich means he will have 2 rounds of surprise)
- 1 attack + 1 bonus attack (2 scimitars) + 1 action surge attack.
- DMG will be: 1d6 (weapon) + 2d6 (sneak) + 1d8 maneuver --> CRITICAL = 6d6 + 2d8 + Dex
- Next round either 2 more attacks or attack + disengage (cunning action) + movement action.

3 attacks with advantage for an average damage of 25-30 would definitively bring down the 2 wizards (the assasin knows who they are) in the very first round. If he wins the initiative he will probably be able to bring one more PC down.

Well, are my maths right?
Would you apply the critical multiplier to the extra damage dice from the maneuver?
Am I right assuming that if they get surprised and the assasin wins initiative he will go twice before they able to do anything?

Thanks for your help in advance.

[Human Paragon 3]

You're not really supposed to fully stat out NPCs with PC stats. You could make this guy easily enough though. Give him whatever ability scores you think he should have, give him 3 sneak attack dice and the sneak attack ability, give him multi-attack that lets him make 2 attacks (dagger and crossbow or two daggers) as an action.

Let him make a dash or disengage as a bonus action.

Give him a 1/encounter poison ability that does 2d6 poison damage on a successful attack. Maybe a 1/encounter fog or smoke screen or darkness attack.


6d8+con HP. Proficiency in Dex and Int saves, stealth, perception, insight, persuasion, and thieves tools.

[Louro]

Yup, I know.
The adventure takes place in a city, so I have a couple of simple NPCs for the "unexpected" situation, with just stats, abilities, attacks and related information they could knew. But for special and important NPCs I do a full (simplified) character sheet.

I like the fog/smokescreen thing :)

[SliceandDiceKid]

Bonus action: dodge

[Callin]

Remember that you can only use sneak attack once per turn. So one big hit and two normal in the opening is still going to hurt. Specially if they use a poison as well. I prefer flying snake venom myself, but that is sure to kill someone. After that action economy is going to be against him.

[Louro]

Oh, you are right Callin, only one sneak per round. This way they will have a chance to survive the encounter, even if the assasin uses some sort of venom (not a yes-no deathly one).
And yes, after the opening he will be in clear desadvantage but his cunning action disengage might allow him to escape alive for future annoyance.

Thanks for the replies.

[SliceandDiceKid]

Oh, you are right Callin, only one sneak per round. This way they will have a chance to survive the encounter, even if the assasin uses some sort of venom (not a yes-no deathly one).
And yes, after the opening he will be in clear desadvantage but his cunning action disengage might allow him to escape alive for future annoyance.

Thanks for the replies.

Dodge action is incredible. Don't forget it.