This card has ludicrous snowball potential. Great for forcing your opponent to burn a silence and I expect there'll be a lot of that in the next meta. Might be worth it even without elemental synergies.
This doesn't just snowball, it avalanches. You HAVE to get rid of it before it gets more than the first Spell Damage +2, because even if left for two turns (Spell Damage +4), you now basically have 4 mana Pyroblasts in the form of Fireball. Three turns and Fireballs have doubled in damage. That's kinda crazy.
That being said, a silence or just killing it isn't that hard of a counter to do, so it's honestly pretty balanced imo