There was sage advice on this oneOr what if the caster moves to a different plane of existence? Which direction is 'away' now?
I've never considered whether a caster could maintain concentration on an effect in a different plane... my instinct would be to say no, but then again, why not? I could see ruling yes if they were in the Ethereal plane, especially if they were still within the general proximity, so to speak, e.g. via blink.
I wouldn't say so. If A wizard casts the spell, and then turns around, it still would move away from them despite not moving away from the direction they are facing. "Move away" doesn't imply any facing rules. It there was a spell that pushed all creatures within 5ft of you 10ft away, they wouldn't all move in the direction you are facing, especially if one of those creatures is behind you as it would require the creature to go through you. Since a cloud of gas is not a single unit or cohesive whole, I don't think there is any issue with it spreading out in a donut shape. Especially since we know that gas can and does act this way. Additionally, if the caster is willing to take that initial damage from the spell and risk losing concentration (if not a conjurer), I would say the player earned it.
I would rule that it would be impossible to be at the exact center of the cloud since that would require the caster to occupy no space or to be a perfect sphere themselves. Nobody is perfectly symmetrical so pick a random direction for the cloud to move in.
Although if you rule differently can I play a wizard in your campaign?![]()
Eh, I don't think anything in 5e rules requires such a degree of exactness. I think if it is "good enough" it is reasonable to assume it will work. I mean, people generally do not occupy exact 5ft cubes of space, but it is a useful abstraction that makes it easier to run the game.
But do you play online? I may have a space opening up when I start running Descent into Avernus within a few months of it coming out.
For better or worse, I'm quite busy and have my hands full just trying to run my home game. So I appreciate the invite, but online games just don't work for me.
BTW there's nothing wrong with playing a (and I'm not sure how to phrase this because I don't want it to sound like a put-down) "shenanigans / exploit the rules" game as long as everyone is on board. While I try to encourage creativity I would just rule differently and not allow a donut-hole stinking cloud. Mostly because it would make my brain hurt.