First, I would like to say that I want those nymphs.
This deck looks really good, actually.
Elite Firefly might work better than cremation, IMO, and would leave you with a constant amount generated for a little while.
The 3 biggest weaknesses of this deck are 1. Shields that Reflect (no kidding), 2. Quanta Denial (but hey, all decks suck against this in general), and 3. the fact unstable gas destroys all of your creatures.
The unstable gases are redundant. Take at least 3-4 of them out. With 3 air nymphs, there is no reason why you should need those. replace them with quints and change the mark to aether. This way, your creatures will be safer.
You should also add some explosions to abuse the perm control of fire.
If you use fire, you NEED to abuse it's power and abusive control against the enemy