Objects from those schools aren't especially susceptible to damage types from their own schools; generally the opposite is true - e.g. Lightning Beetle has Lightning -2, Fire Demons have either Flame -2 or Flame Immunity, Devouring Jelly has Acid Immunity, etc. I can't think of another example (besides these Poison conjurations) where a card belonging to a specific elemental school is susceptible to a damage type associated with that same elemental school.
Devouring Jelly has no resistance to Hydro (and isn't Water school anyway). Lightning Beetle has no resistance to wind. Screech Harpy, Galador, and Whirling spirit have no resistance to Wind or Lightning, despite being Air school. I think you might be mixing up Schools and Subtypes.
We're generally on the same page. I'm not suggesting every object belonging to an elemental school or having a certain subtype should have some resistance or immunity to a damage type associated with that school. But I am suggesting it is odd - in fact, unprecedented - that an object belonging to an elemental school is particularly susceptible (e.g. has the Damage Type
+X attribute) to a damage type associated with that same school, as in the case with Poison Gas Cloud / Wall of Poison Gas.
My bad on bringing the Jelly into this; for some reason I thought it was Water school (and hence made sense that it has Acid Immunity, where Acid damage type is generally associated with Water school - see Acid Ball). But that's fine. There are oodles of examples of non-elemental school objects like the Jelly that have resistance and/or immunity to a particular damage type or spell attribute type that is associated with a different (elemental) school.
Clouds are associated with air because they are gaseous, not because they are specifically made up of air. The four classical elements refer as much to the 'nature' of an object as to its composition, i.e. Earth is solid, Water is liquid, Air is gaseous, and fire is variable/incorporeal. Since poison clouds are gases, the Air school does seem the most appropriate, as others have mentioned.
Yes, I see what you're saying... although I'll still contest that clouds are generally composed of small droplets of liquid (or solid particulates, in the case of smoke), not gas. In real life, a poison cloud would likely be comprised of water droplets with some dissolved toxin. Hence I suggested that poison cloud could just as easily be Water school... which would make me less argumentative regarding it being susceptible to Wind damage; e.g. a damage type associated with a different school, Air. However, a gaseous cloud of poison could still be naturally occurring: hydrogen sulfide, for instance. Besides, they already put the word "gas" in the title, so I guess it's a little late to debate its phase of matter.
The dark school does indeed have quite a bit of poison, but its spells that deal poison damage are evil in their very nature; demons, undead abominations, and altars to corruption and evil. Poison gas is just a natural phenomenon - a deadly one, perhaps, but so is much of nature, and deadliness is not the same as evil. That isn't to say that the Dark school would be inappropriate, but sorting cloud spells of this sort into the Air school is perfectly fine.
A gameplay/balance reason I bring this up is that it's easy to build a Flame-based Wizard or Warlock using mostly in-school spells, or a Light damage based Priest(ess), and based on promos it looks like a Wind damage based mage will be easier soon, too. But it's much more difficult to build a poison-based mage (including Air Wizard) using in-school spells because no mage is trained in Dark + Air. Yet the poison-based enchantments are Dark curses (e.g. Ghoul Rot, Poisoned Blood), poison-based creatures show up in a few schools but especially Dark (e.g. Darkfenne Bat, Plague Zombie, Ichthellid Larva, Venomous Zombie, Malacoda, etc; let it be noted there are also several Nature creatures that deal poison counters including Oscuda, Emerald Tegu, Death's Head Scorpion, Giant Wolf Spider, etc), but poison-based conjurations are split between Dark and Air (e.g. Idol of Pestilence, Altar of Skulls; Poison Gas Cloud, Wall of Poison Gas). And many of these are level 2 or higher (Ghoul Rot, all the poisonous creatures aside from Darkfenne Bat, all of the conjurations including the wall). This makes for an expensive archetype.
