70+ damage from a single attack at third level

[Matrota]

So I was reading Xanathar's and realized something while reading over the Grave Domain cleric. Their channel divinity ability allows them to bestow vulnerability to the next attack received. This caused me to think of a particularly nasty combo. At third level, the grave cleric of the party channels this ability on the unsuspecting target. Then, a bugbear assassin rogue surprise attacks them wielding a rapier. Since the enemy is surprised, the sneak attack is an automatic critical hit, and it also permits the usage of the hobgoblin racial surprise attack ability. At 3rd level, this is 1d8(rapier)+2d6(Sneak attack)+2d6(surprise attack). It is then doubled to 2d8+4d6+4d6 since it is a crit, and the total damage of this attack is doubled due to vulnerability. Assuming the rogue has a +3 dex modifier, then the average damage for this attack is 70. Is this a correct reading on the rules, or have I misinterpreted something? How would you react if someone pulled this off in a campaign you were in?

[OvisCaedo]

It's a lot more finicky to pull off than it might seem, because of how surprise rounds actually work. Namely the fact that there is not actually a surprise round, just things being either surprised or not until their first turn. Technically, on a surprise attack, an assassin won't actually get their bonus crits if they lose in initiative, even though the enemy has to skip that first turn. Pulling this off would require both the cleric and assassin sneaking up successfully enough to launch a surprise attack, and then both beating the enemy in initiative.

Or it could go some other way depending on how your GM actually decides to run things, and when they decide initiative starts and how sneaky or not the Grave (not death) domain's channel divinity is.

[Jerrykhor]

By RAW, they need a specific initiative order to make that work. The cleric has to go first, get within 30ft of the target, use the Channel Divinity, then Bugbear rogue next, and lastly the target. If the target has higher initiative than both of them, it won't work.

Its fine.

[Ventruenox]

Given how the Rogue is likely to beat out the Cleric on the initiative rolls, he could probably use his reaction to ready his attack to go after the Cleric in the initiative order.

[Quoxis]

Just a little correction on nomenclature: Xanathar’s guide had the grave domain which i believe you’re referring to, while the death domain is in the dmg. Just to avoid confusion in the future.