OK. My turn.
I don't care who you are, 2 damage to all ENEMY creatures at a 2 cost activation is... well... ridonkulously over powered. You could make the initial cost really high and it still pays for itself in the long run. For the sake of balancing, if you're doing damage specifically to Enemy Creatures, increase the activation cost to 3
.
On a different note, Fire already has so many options for controlling enemy creatures. Why not take this card in an entirely different direction?
Possibilities could include:
2 Destroy 1 random Permanent on your enemy's field - Initial play cost could stand to be cheaper if you've got explosion on a stick
2 Deal 3 dmg to the enemy's HP. A very slow damage on a stick permanent, but in large numbers with enough quanta... this could be trouble
2 A random enemy creature gains -1/+0. Affecting a creatures attack is something that hasn't been utilized much yet.
IMO, too many people associate fire with destroying creatures en mass. I'd like to see a lot more ideas popping up that involve other venues for fire to take advantage of. You could come up with a lot of different things for a Volcano to do, these were just some of mine.