Can a druid use Wild Shape in mid-air to survive being dropped?

Question

Our group is all relatively new to D&D.

Let's say that an aarakocra picks up a dragonborn druid, and carries her up to an altitude of 125 feet. It would take her ~2.5 seconds to hit the ground when she's dropped. Would she have enough time to use Wild Shape during the fall to turn into something that would survive the fall?

She wanted to be a mouse, which can theoretically survive a fall from any height due to its low terminal velocity. She also could've changed into something with a huge number of hit points and tanked the fall damage.

Our main question is about transforming into Wild Shape in mid-air. We could not find any solid info on the time it takes for the change in the rules (5e).

Can a druid use Wild Shape in mid-air to survive being dropped?

Answer 1

Let's break this down in to Rules As Written, then I'll give a nod to Rules As Fun. But the important thing to start with is this: D&D is not a Physics Simulator (alternately, it is a hilariously bad physics simulator).

Rules As Written

Falling

The rules for falling are as follows:

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.

That's it. No modification based off size exists. Yes, realistically, a small enough animal would have a low enough terminal velocity to avoid harm--but D&D has no consideration for that.

As for the time it takes to fall, the rules are somewhat expanded upon in Xanathar's Guide to Everything (p. 77):

The rule for falling assumes that a creature immediately drops the entire distance when it falls. But what if a creature is at a high altitude when it falls, perhaps on the back of a griffon or on board an airship? Realistically, a fall from such a height can take more than a few seconds, extending past the end of the turn when the fall occurred. If you’d like high-altitude falls to be properly time-consuming, use the following optional rule.

When you fall from a great height, you instantly descend up to 500 feet. If you’re still falling on your next turn, you descend up to 500 feet at the end of that turn. This process continues until the fall ends, either because you hit the ground or the fall is otherwise halted.

Here, these optional rules state that the moment you begin falling, you immediately descend 500 feet. No consideration is given to acceleration, you just immediately drop 500 feet, then do it again at the end of your next turn.

Thus, per the Rules as they are written, it does not take time to fall, so (unless you have something like Feather Fall that explicitly interrupts a fall) there is not time to do anything at all before you hit the ground, unless you are falling more than 500 feet and your DM is using the optional falling rule.

And even if there was time...

Wild Shape can only be used on your turn

The rules for Wild Shape are as follows:

you can use your action to magically assume the shape of a beast that you have seen before.

And actions are taken on your turn:

On your turn, you can move a distance up to your speed and take one action.

Thus, unless it is the druid's turn when the aarakocra drops them, they can't Wild Shape... because Wild Shape requires an action, and you can only do those on your turn.

How to Wild Shape when dropped anyway.

An aarakocra that has grappled you cannot cross 125 feet in a single round:

When you move, you can drag or carry the grappled creature with you, but your speed is halved, unless the creature is two or more sizes smaller than you.

So, assuming the aarakocra (which has a fly speed of 50 feet) uses its Action to Grapple you, in a single turn it can only lift you 25 feet off the ground. It may then Dash on subsequent turns to cover 50 feet per turn. Thus, it would take 3 full turns for the aarakocra to lift you to your intended lethal-drop height.

During this time, the druid may opt to use the Ready action:

First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger [...] When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger.

So, on their turn, the druid declares that they wish to Ready an action to Wild Shape into a mouse if the aarakocra lets go of them. So, the aarakocra lets go, and the druid activates their reaction to Wild Shape (which happens immediately after they are dropped (the trigger), thus interrupting the fall).

But, RAW, it won't help...

The falling rules have no allowance for variable terminal velocity. A falling dragon and a falling mouse take the same exact fall damage.

Rules As Fun

Situations like this, especially as you've described it, are one of the reasons why DMs are fully permitted to ignore, alter, or make up rules on the fly. Per the description of the role of the Dungeon Master in the DMG (p. 4):

The D&D rules help you and the other players have a good time, but the rules aren’t in charge. You’re the DM, and you are in charge of the game.

In a case like this, I would want to reward the player's creativity and roll with it. Ignore all the nitty-gritty rules that are (for the moment) interfering with fun, and let the player have a creative solution to this problem.

Answer 2

It’s up to the DM, but it probably still works.

I’d allow it. But it isn’t clear exactly how it should work because nothing about falling is particularly clear in the rules. Let’s hit those rules first

From the PHB:

A fall from a great height is one of the most common hazards facing an adventurer. 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

This is all we have in the PHB, and it is totally useless for ruling on your situation. We get more detailed in Xanathar’s Guide to Everything:

When you fall from a great height, you instantly descend up to 500 feet. If you’re still falling on your next turn, you descend up to 500 feet at the end of that turn. This process continues until the fall ends, either because you hit the ground or the fall is otherwise halted.

Your fall is only 125 feet, so Xanathar is similarly unhelpful.

There simply is nothing in the rules that helps us - the action economy of falling is not explained.

Rule of Cool: Animals falling from the sky.

This is a really clever solution to a problem, and it is a solution that has been used at my table before. In the absence of clear guidance, go with the most fun ruling. Animals falling from the sky is always the most fun ruling.

This is just feather fall but worse.

It’s not a balance issue. Feather fall exists and makes falling entirely trivial for the whole party. This makes falling survivable for one party member. Also animals falling from the sky.

Whatever the rules are, you can probably still pull this off.

125 feet is pretty high. You’re probably going to get a turn in the air on the way up. If this is the case it probably doesn’t matter what the DM wants to rule about falling: you can ready your action to wild shape when dropped. This allows you to wild shape in response to being dropped, and will have you hitting the ground as a woodland creature of your choice.