Looks good.
Moving to the breath weapon, lets deal with poison vs scalding first. Based on the original text, I'd say that the poison breath should be a smallish amount of untyped damage plus unconsciousness (immunity to poison negates; Ref save halves damage and negates unconsciousness)
Alternatively, we could have the poison vapour do acid damage (similar to how early-edition Green Dragons breath poisonous chlorine gas that did hit points damage) or Con damage.
It could actually
be a poison that causes Con damage plus unconsciousness as its primary/secondary effect.
Or we could have it do a bit of damage (untyped or acid) and expose creatures who fail their Reflex saves to the poison (Fort save to avoid unconsciousness)? Or maybe have them make the saves separately?
, while the scalding breath should be a normal-large amount of fire damage plus blinding (Ref save halves damage and negates blindness).
That approach to the Scalding Breath sounds fine.
As for the gaseous form breath, I feel like we have a precedent somewhere, but I guess it's pretty much straightforward anyway. I might give a Fort save rather than a Ref save for that, though. What do you think?
Regarding the gaseous breath, I suspect you were recalling the following:
Breath Weapon (Su): A Mystaran sapphire dragon has two breath weapons: a line of lightning or a line of vaporizing energy that does untyped damage. Any creature or object within the area of effect can attempt Reflex saves to take half damage. If a creature struck by the first (vaporizing) breath weapon fails this save they must also attempt a Fortitude save or contract a supernatural curse carried by the breath weapon, as follows.
Sapphire Curse: Objects and creatures affected by this curse turn into vapor as if they were affected by the
gaseous form spell. This vaporous condition lasts for 1 minute per age category of the dragon. Normally, the vaporous creature or object returns to solid form at the end of this duration, but if the vaporizing breath weapon did enough damage to destroy the creature or object it will dissipate into gas and a few puffs of dust when the duration expires. The traces of dust are enough to restore a dissipated victim with a
resurrection spell.
The sapphire curse can be neutralized by a
dispel magic,
remove curse, or
break enchantment effect that succeeds at a caster level check against a DC equal to the dragon's spell resistance (minimum DC 15). A vaporized victim can also be restored by any effect that can transform a gaseous object into a solid one, such as the
polymorph any object spell or a vampire's
gaseous form ability.
The above Sapphire Curse is a pretty exact match, so we just need to tweak the name and text a little (I think "Vaporizing Breath" works better than "Vaporous Curse" in this case) and decide on a duration for the effect.