I've noticed this on several submissions for the Gallery:
If you have X (or any other variable) anywhere on your card, you MUST include a definition for it (generally in the identifiers). Don't put X on there if you have no meaning for it as then it's just undefined and confusing and not at all realistic. I've been voting these down because they are broken (not broken as in outrageously overpowered but broken as in doesn't work). A lot of them have been otherwise good cards, but without a meaning for X the card itself is unplayable.
Here are some real card examples of X definitions:
X = # of female N.T. Heroes in play
X = # of Assyrians in play
X = # of your Genesis Heroes in play
X = # of captured characters in your territory
