MArcomage

The concept is that you mass up zombies and corpses in front of your wall to act as buffers against an impending attack. It's a last resort card in case you are left with no defenses.
I was testing my Undead deck recently and I observed that I mostly received Undead cards instead of +Wall and +Tower cards. I changed my deck several times but still very few times did I receive a building up card, thus leaving my tower and wall to my opponent's mercy. Of course, Undead cards can be very powerful attacks, but you need massive resources, and an Undead deck never uses up bricks for the exact reason that you can not have many other cards in your deck except Undead, if you want to achieve a good result.