The main problem I see with this card isn't the resistance to permanent control, it's the fact that it only requires fire quanta. This card has only two downsides compared to Unstable Gas:
1) By itself, it requires time to go off.
2) Does not damage enemy creatures.
#2 is irrelevant when going for a quick kill, and #1 is made irrelevant by Explosion. So what you have here is an Unstable Gas that cannot be stopped except by reflective shields (PC from the enemy will just make it go off anyway), and requires less quanta, of only one element. Healthrough is not necessarily a viable counter, as five of these could be played at the same time, creating a time bomb for 100 damage at once.
It has weaknesses, sure, but only three - the two above cards, which most decks do not carry, and an out-rush tactic. This card is thus unstoppable by any non-rush that doesn't carry reflective shields. Pair it with any decent stall tactic and you can also stall rushes long enough to beat them.
My conclusion: this card forms stall-burst combos that can only reliably be countered with reflective shields. It needs a nerf. My suggestion would be to add a requirement for another element, but that is too similar to Unstable Gas. I'm at a loss right now.
