falling details

[kyaldo]

hey people.
i have looked but haven't managed to find an answer for my required details on falling in 5e.
what i particularly want to know, is A) how fast and B) when does a character fall.

allow me to provide 2 hypothetical combat situations that each share the following facts:
there are 3 characters (A, B & C) in combat.
character (A) has an initiative score of 20, character (B) 15 and character (C) 10.
they are each standing on separate 5' square floating platforms 900' above the ground.
the platforms are slippery and the players know that if their character takes damage whilst on the platform, they will need to make a dex save.
on a fail, they fall off of the platform, plummeting towards the ground.
each platform is 20' away from the other 2.

situation.1

initiative 20:
character (A) fires magic missile at Character (B)
character (B) takes damage and fails his save (so he falls)

initiative 15:
character (B) casts fly, so as to make his way back to his original platform.
when he has finished casting the spell, but before he begins the movement granted by the spell, how far is he from his original platform?

situation.2

initiative 20:
character (A) casts magic missile at character (C)
character (C) takes damage and fails his save (so he falls)

initiative 15:
character (B) wants to cast magic missile at character (C). as character (C) has not yet started his turn, has he began falling or is he still 20' away from character (B)?

i hope that i have made this clear enough for somebody to tackle for me.
thanks.

[Man_Over_Game]

Xanathar's covers this explicitly. It says:

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.

So immediately after step-off, you're 500 feet down. At the end of your next turn, if you're still falling, you're another 500 feet down.

So in both situations, they're 500 feet down during their entire turn.

Player B would stop falling at the 500 feet mark, since Fly would counter the falling that'd occur at the end of his turn.

Player C would continue falling, would be out of range for Magic Missile (at ~500 feet away), and would hit the ground at the end of his turn at 900 feet.

This is why Featherfall has a Reaction time, so you can split second counter the falling speed. If Player C had Feather Fall prepared, he could have used his reaction to reduce his fall speed to 60 feet rather than 500 feet, he would have started his turn at ~80 feet, and he'd be within range for Magic Missile.

[kyaldo]

brilliant. thanks.