It depends on how you define 'across'.
And if you do allow vertical movement, I wouldn't make it a better version than a fly speed. It should still cost extra movement speed for the vertical movement.
Hey all,
A player of mine wants to take the Cloud step feat and describes wanting to go straight up into the air.
The feats reads as "walk for brief stretches across insubstantial surfaces." and "move across water, air, and solid surfaces that can hold only limited weight as if they were normal ground." both of which seem to imply horizontal movement or perhaps at some angle.
I have read arguments that other classes/feats get fly speed at a similar level to Cloud step, therefore Cloud Step should allow movement in all directions as well but that's really not how the feat is written.
Does Cloud Step really allow complete vertical movement without difficult terrain as Fly does("Moving upward (straight up or diagonally) uses the rules for moving through difficult terrain.)?
I don't think you should rule it as "Fly". You should rule it as "Air Walk" (https://2e.aonprd.com/Spells.aspx?ID=6). Which is pretty much the Spell version of Cloud step.
So, no, allowing the Rogue to walk straight up isn't a good way to handle this.
I agree with the above poster you should basically treat it as a limited form of Air Walk spell.
How does it differ (IMO) it only functions while you are striding, meaning you fall at the end of your turn. However, it doesn't have a set duration and you can do it each turn as often as you want.
All of which is to say, you can ascend or descend at a 45° angle, and I think going up would count as difficult terrain.