What is Jovian Thunder?
Jovian Thunder is a rare, extremely powerful overall Combat (Attack and Defense) Bonus for your Troops. It increases your Troops' Attack and Defense ratings by 80%!
Jovian Thunder does not stack with other Combat Bonuses. Once you apply Jovian Thunder all other bonuses are deactivated during its two-hour duration. Although it does not stack with other Combat Bonuses, it still combines with the Combat Bonus the General you're using provides.
Also noteworthy is that, while Jovian Thunder is active and all other combat bonuses are made inactive, their timers are still going. For example, if you have 4 hours left on a Mars' Blessing when you use a Jovian Thunder, there will only be two hours remaining of the Blessing when the Jovian Thunder item expires. And, again, during those two hours, Mars' Blessing has no effect whatsoever.