Some cards have in their descriptions condition, instead of exact values. Now we have seen armor and gold modifications. Some testers confirmed an opportunity of unexpected use.
Rend Armor – allows to modify unit’s amor with the same negative value. It could be used to zero heavy armored enemy at first sight. But @EosinDota tried to use it on unit with negative armor. And final armor will equal to zero (-2 + (- - 2) = -2 +2 = 0). It’s very usefull in combo with Double Edge which dramatically reduce allied unit’s amor in exchange for an attack.
Shop Deed – reduces every item in your Secret Shop by its base cost. Again, we are waiting for a fully free shop. So we just need to collect 22 gold to by this card and then take items without fee. But mechanic of this card allows to use it twice and items gain «bonus gold». So they will have negative price and our gold will increase for their base cost every time when we buy it. It's very good in combo with Mercenary Exiles and Revtel Convoy, which attack and health abilities depends on your gold amount.