No. I’m pretty proud of my mastery of the OL system, I’m gonna double check after writing just in case, but the only thing that is mentioned would be in Chapter 8.
It talks about “Ad Hoc Damage” Environmental effects and hazards and what have you in or out of combat that can either deal normal or lethal damage.
That rule deals with dealing damage, but it doesn’t deal with dealing banes, but you could potentially make it deal banes too. Something I have never considered before when using Ad Hoc.
I wanna try it out some time soon now…!
You could make Ad Hoc deal banes, or deal damage (lethal or not) AND banes of certain types and power levels depending on severity.
And about the example with the gas cloud, the environment can always be as much of a player during combat. A neutral party that doesn’t discriminate.
There’s the obvious difficult terrain that costs double the movement but you can do anything with the environment!
In the case of your gas cloud–
You could rule out that a certain section of the field of combat has a gas cloud. Play it like you would any invocation of the Barrier Boon, An area of combat that if you willingly enter or end your turn in, you could be subject to a bane attack and such.
Making it deal a Sickened bane attack every round as long as you’re there seems a little too much considering how other lasting area effects work.
General rule of thumb maybe, but if you have an effect that persists in an area, make it so that it only applies when creatures willingly enter it or end their turn there, because that is how Barrier and Aura works. Maybe these toxic clouds could even be dispelled permanently or temporarily with a Nullify bane just like any old Barrier boon if you’re nice.
Another way I could see you potentially run this gas cloud thing is if these clouds of gas are because you’re in some biohazard factory thing, theres pipes leaking these gas and every random d4 rounds, anyone who is in a cone area projecting out from the pipe will suffer a bane attack from the pipes spewing out these clouds! Having proper biohazard suit thingies, the Sustenance boon, or maybe the Resistance boon are the ways one could avoid the hazardous effects of those broken pipes!
As I already mentioned, you can always make the effects be special and somewhat different too!
The Sickened bane inflicted by the clouds is potent and you have disadvantage to resist! The Sickened bane also deals 1d6 damage at the start of your round! Or this Sickened bane is actually extra powerful and gives a -2 penalty to defenses and disadvantage 2 instead of the usual -1 and disadvantage 1!
It’s always up to you, just be fair and at the same time, equally cruel! mwahahaha!!!