Without getting fancy, 6x this/CP + 3x discord +15x tower seems overly strong. Repeatable CC is a rare and valuable commodity in EtG. For example, after you account for the extra attack and HP, a parasite isn't much cheaper, but immensely less effective. It can't be easily boosted either. An easy way to fix this without messing with the idea too much would be to increase the cost of fire cannon.
Now, on the other side... Fire and entropy is an unused combo. So while promoting unused combos is great design, fire and entropy aren't used together for a reason. They have no synergy. A couple cards, (such as rage potion and explosion) are still useful in a duo with both elements, but most cards are redundant. The main power of this duo is going to rest on one card. That means that it's probably okay for chaos cannon to be stronger than an average card. The balance should be just about right then, which is impressive.
As a side note, to maintain consistency with other cards, the effect of adrenaline would probably not be to have the cannon attack creatures four times, but to have it attack creatures once, then go for HP. At least, that's baisically how adrenaline works with dive.
