MArcomage

Deny, Zero cost, Rare
Quick. Durable.
Tower: -10
Replace random uncommon or rare from enemy hand with a common card

At the cost of 10 tower and since it would stay on hand, I'd probably be unhappy to draw this in anything but a building deck. It could be used in desperation if you're in a building race and need to knock out a card for 30+ tower, but with random targeting I'd figure it would be most likely used to decrease your own tower so you could follow it up with a card that favors having a lower tower. Even in that scenario, you're not likely to make up the 10 tower difference. (Maybe Jealousy alone, putting yourself below 50 so you can decrease your opponent by 25 rather than 10?)

To improve upon this, I think the targeting should be smarter (Rares first? Manually select the card to be replaced?) and/or the tower hit should be decreased.

I agree. Make the discard targeted, and this card becomes a lot more interesting.

I understand your objections, but it's Quick/Durable -- doesn't that count for something to ensure you hit your target?

Unless the opponent deliberately floods his hand with uncommons and rares, usually only four or less of the cards in their hand will be noncommon at any given time. Using Deny once gives a 25% of getting rid of the card; a second use immediately afterward gives you a 1/3 chance at removing the card you need to get rid of.

I know the non-targeted nature may be annoying when used, but I was hoping to get around that by making it Quick/Durable/0-Cost, allowing it to be used as many times in a row as would be needed. Given that that is how I tried to make the card work, what tower loss do you think would be fair for both the player of the card and for the opponent hurt by it?