Carrion crawler, Common, 4g3r
Undead
Attack 3
If opponent discarded a card last turn,
Attack 10
This has been argued before with another card concept, and my personal opinion on it hasn't changed. Having a card that punishes an opponent for discarding is unfair and not fun. For every other punisher, the opponent has a choice to either take the action or not to. You can always avoid actions such as increasing your wall, dealing damage, or playing a card from a particular position. Arguably, the opponent is also in control of the results of accumulating too much of a facility or resource (over time, not necessarily in one turn).
However, it is too easy for a player to actually force his opponent to discard. Brigand, Aqua, and Destruction are all very effective in causing the opponent to have no choice but to discard, not out of a desire to clear unwanted cards from the hand or to conserve resources for a finisher or to enable another card's mechanic such as Vulture, but because he literally cannot play any of his eight cards.
This kind of match tends to be long and tedious. Giving the player using this strategy a low-cost, hard-hitting Common would be detrimental to MArcomage as a whole. We shouldn't punish for what is, essentially, the "Lose a Turn" option.