Beings of Tash Kalar
Obviously, a tower with a cannons on its top, aiming in both directions.
A shot so powerful that it pierces through the first piece and destroys also the second piece in its way. Unless any of them is legendary. Color does not matter – like all gunpowder cards, the Tower does not recognize friends and foes.
Destroying power is obvious. Empire is great at attacking enemy pieces from distance (Cannon, Gun Tower, Hypnotist).
Another advantage of the Gun Tower is, that after you have the pattern ready, you may summon the tower at 8 different places, getting the heroic piece at the space where you need it most.
This is another of the Empire gunpowder units, and I imagined it originally to be built and operated by dwarves. But it works well even now, when Empire got a bit less less Warhammerish and a bit more Chinese feel.
Originally, it was even stronger (destroying three pieces), but it was so intimidating we had to change it. As you cannot give advices like "never line three pieces in a row" :)