Just an alternative that leaves out the X: "Deal 1 damage to your opponent for each creature you control. Enemy creatures lose 2 HP."
Comparing to Unstable Gas: Your opponent doesn't have a way to stop it unless they know its coming and use mass creature control. Also unlike UG, it only requires 1 element to use, though creatures are needed for its effectiveness (it's sorta like the Hope of damage spells). I don't think the 9 cost is enough to keep it from being overpowered.
A devastating deck: 6 Gnome Gemfinders, 6 Fractal, 6 Overrun
EDIT: Reformatted for clarity.