Would igniting an Unstable Gas drain all and ?
Unstable Gas doesn't target, so neither.
Well, Quintessence doesn't allow a creature to be
targeted by any skill or spell, and if an enemy creature is immortal and you ignite an Unstable Gas, it won't take damage. It only protects against being targeted, and it protects against Unstable Gas.
Same with RoF and Plague.
You never actually "target" a creature, but instead, you automatically "target" all of them. (I think, at least.)