Would it be possible to launch an ambush from inside a space created by the Rope Trick spell?

Question

I am currently a fairly new player who's throwing their innocent Wizard into the maw of the beast. As I am still learning and getting used to the rules and tactical play I would like to confirm a few things about the Rope Trick spell.

The Rope Trick spell states the following:

(...) The rope can be pulled into the space, making the rope disappear from view outside the space. Attacks and spells can’t cross through the entrance into or out of the extradimensional space, but those inside can see out of it as if through a 3-foot-by-5-foot window centered on the rope. (...)

To me it sounds like these two conditions make it possible for a party hiding inside of the rope trick to ambush an unsuspecting patrol passing under the rope trick.

Also Falling mentions:

(...) At the end of a fall, a creature takes 1d6 bludgeoning damage for every 10 feet it fell, to a maximum of 20d6. The creature lands prone, unless it avoids taking damage from the fall.

For this tactic I have made a few assumptions:

• If the rope trick is less than 10 feet high the party can avoid fall damage.
• Dropping down and attacking can be done simultaneously.
• The party will gain a surprise round upon execution.

Aside from these assumption I also failed to find any information on Plunging Attacks. So I would like to know if this even a thing at all (to let our Barbarian and Druid look extra cool in return for assisting me in my madness).

Answer 1

If the rope trick is less than 10 feet high the party can avoid fall damage.

That is correct. As you have already pointed out in your question the party will not take any sort of fall damage as long as the height is no more than 9 feet. (Unless there are sharp objects or otherwise damage-capable objects below you in which case it's up to the DM's discretion).

Dropping down and attacking can be done simultaneously.

Dropping counts as a free action. To my knowledge, there are no rules regarding dropping that state it is an action.

Remember that 9 feet are still high enough in some situations to make you prone. (It really depends on the terrain and whatever is below you but keep that at the back of your head).

Attacking while falling has no official rules. I would say that combat rules apply as normal.

Plunging Attack Houserule: While falling, you make a Melee Weapon Attack against a target. On a hit, you deal the weapon's damage plus additional damage equal to 1d6 for every 10 feet you fell, and you take half the normal falling damage. The additional damage is the same type as the weapon. (Credit)

In my current campaign, the party has a half-elf warlock, a dwarf barbarian, an Aarakocra druid and a drow rogue. The rogue is a huge fan of assassin's creed and most of the time when I describe a possible combat encounter he usually runs away, hides and tries to find a way to air assassinate the target(s). Every single time I use this house rule as it seems very logical to me with the exception that I also ask the rogue to make a dexterity saving throw in the case that the height is more than 20 feet. If he succeeds he takes half the damage as described in the rule otherwise I describe how the way he falls damages him.

The party will gain a surprise round upon execution.

Just a quick note: There is no such thing as a surprise round, it's a "surprised" condition that makes any surprised creature lose their first round.

The target(s) will be surprised as long as you roll a Stealth Check and everyone's roll is higher than the target(s) passive Perception according to the official d&d rules.

"If neither side tries to be stealthy, they automatically notice each other. Otherwise, the GM compares the Dexterity (Stealth) checks of anyone Hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn’t notice a threat is surprised at the start of the encounter."

(Emphasis mine).

Answer 2

The concept is fine

... the details are a little off.

Surprise affects creatures, not rounds

The DM determines who might be surprised. If neither side tries to be stealthy, they automatically notice each other. Otherwise, the DM compares the Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn't notice a threat is surprised at the start of the encounter.

So, you are hiding in the Rope Trick - this is no different from hiding in the wardrobe or, for that matter, in the shadows. Your party makes a group Dexterity (Stealth) check. Because a Rope Trick is a very good place to hide, your DM may allow you to make this check with advantage (I would). This ability check sets the DC that the opposition will need to overcome with the passive Wisdom (Perception) to avoid surprise.

But, I hear you ask, if I can't be seen, how could the perceive me? Well, you are a adventurer in a fantasy medieval role-playing game so you haven't had a bath in 2 months so basically - you stink. The Rope Trick hides you from view and stops attacks but it doesn't stop your stench. Similarly, your fighter friend shakes nervously whenever he's waiting for action so if you can hear his chain-mail jiggling so can the guys you want to ambush. All of this random stuff is what the ability check represents.

Now, if the people who you want to ambush rely predominately on sight to perceive things (most creatures do) they will have disadvantage on their Perception checks. So assuming at least half of you roll somewhat decently you have a good chance to surprise most creatures.

Falling

Falling is instantaneous and if you don't take damage, you remain standing. If you fall from less than 10 feet you don't take damage so that all works.

There are no rules for a "death from above" type of attack. A kind DM may give you advantage on your first attack - I'm not that kind.

Initiative

After surprise is determined and before anyone does anything initiative is rolled. The mechanics of surprise have been dealt with at length in numerous questions.

Attacking and Movement

Attacking and movement are "simultaneous" in that you can do both on your turn. Mechanically, movement can be interrupted by attacks (or spellcasting, hiding etc.) so you can move, fall, attack, move, attack, move etc. which are each resolved sequentially but are narrativly a series of fluid interconnected motions. Its analogous to the fact that dancing is more than following the dance steps - D&D uses the steps to resolve the action but in "reality" its all a seamless whole.

Looking 'Cool'

Is more about how you interpret and narrate the results of the dice and less about what the dice actually say. The dice can tell you you hit for 12 points of damage and sometimes that's what you will say and that is perfectly fine. However, its more cool to see the result and say - "With a primal yell, Thugnar steps out of the Rope Trick and plunges on the unsuspecting rabbit. Before it has time to let out a squeak of terror, his greatsword enters its back and tears through fur and flesh with a spray of blood. It takes 12 points of damage. Is it dead?"