Darkness and Surprise: how to rule it?

[Citan]

Hi all!

An answer to another thread made me consider a case that I wouldn't know how to rule out (never played an Assassin, have some trouble understanding how to manage Surprise in some creative situations).

Consider this.
You're a Shadow Monk 6 / Assassin Rogue 3+. You have 1 enemy scout in the plain in front of you looking broadly in your direction. For now you're Hidden, but you cannot close the distance without him seeing you for whatever reason. The weather is very cloudy.

Q1
If you...
a) Cast Darkness just under the clouds, above your enemy.
b) Use your Shadow Step class ability to teleport there...
c) Then fall on your enemy with your finesse weapon ready to strike...

How should the situation be ruled?
Should the Rogue roll a DEX check against Passive Perception as soon as Darkness clouds appear?
Or just roll for when he's falling down?
Or do you just consider that enemy is surprised, plain and simple?

Q2
Also, if the Rogue could instead reach the enemy with Dash and did it instead, would you consider that it automatically lose Hidden status so no chance to gain Surprise? Or would you say that, considering the short span of time (<6 sec), Rogue can still try to roll a DEX check to gain surprise (with maybe disadvantage)?

Thanks for your advice.

[Daishain]

My take: (bear in mind that I consider the rules a starting framework rather than the be all end all, another DMs judgement is likely to be quite different)

-If we assume that there's nothing for the sentry to notice in regards to the Darkness casting (emanation made no noise and made no changes to his field of view), then there's no perception check at that time
-If the sentry is occasionally looking around like he should be, I'd give him a low chance of doing so at the wrong moment (probably a 1in20 for simplicity's sake), if he does, he'll notice the dark globe, no perception check needed, whether or not he can do anything about the plunging attack would then be a matter of further adjudication.
-I'd make the rogue do a stealth vs PP check upon shadow stepping, there's bound to be some noise involved.
-If noticed at that last stage, by RAW the attack would no longer be a sneak attack, since it is technically made after breaking stealth. However, I find this unrealistic given the setup, and would rule it using a modified initiative check, with the sentry rolling at disadvantage (essentially modeling how quickly the sentry can go on the defensive). If the sentry loses, the 'death from above' maneuver is a sneak attack as normal. If the sentry wins, he is still attacked first, but it is an ordinary melee attack, no SA bonus

Concerning the latter case, no chance. A couple of seconds provide plenty of time to go on the defensive

[Demonic Spoon]

Surprise and attacking from hiding are different things. The former lets you act in the first round of combat; the latter gives you advantage on an attack roll.

In the scenario you describe, there's nothing subtle about your approach for either option - you will not be hidden at the time you make the attack, so you do not get advantage on the attack roll.

However, before you started charging, your opponent didn't know you were there - therefore, he would be surprised and he would not get to act in the first round.

[Kryx]

Surprise and attacking from hiding are different things. The former lets you act in the first round of combat; the latter gives you advantage on an attack roll.

In the scenario you describe, there's nothing subtle about your approach for either option - you will not be hidden at the time you make the attack, so you do not get advantage on the attack roll.

However, before you started charging, your opponent didn't know you were there - therefore, he would be surprised and he would not get to act in the first round.
Exactly this. Consider surprise like a surprise round from 3.X. It cannot happen in the middle of combat.

[Citan]

With your three detailed answers, the specificity of "Suprise" is now clear to me.

Thank you very much :)