MArcomage

If, for example, you sustained 14 wall damage and 4 tower damage, then the opponent's highest resource would be reduced by 18 (or, if less than 18, reduced to 0).

I'm open to balancing suggestions for this. I don't want to give it a cap, but I don't want to make it too expensive, either. I also don't play Destruction often enough to know how this balances with respect to the keyword.

Maybe half the stock reduction? Or reduce random resources instead of stock?

I don't really play destruction either but I think this card is quite potent and cheap for its damage effect. Also it's an Uncommon, which means you can play it, the enemy loses a lot of resources, and then you play a common Destruction and the enemy loses a facility, or even more resources.

Ofcourse, there is a condition to limit the card, but come on. There's always damage on your wall

There is always damage to your wall, yes, but I doubt anyone will play this at the cost of ten gems just to destroy five bricks. It would be saved for a substantial attack, at which point the opponent's highest resource is probably not his most important one.

And to keep terminology clear, there is no stock reduction. It attacks a single resource.