An asymmetrical creature is a creature which is not symmetrical on its two sides, an example of this is a creature with one arm on one side of it, or 2 eyes in normal places, and another near a place where its arm is, but not on the other arm.
Many concept images showed asymmetrical creatures were possible. However, upon the release of Spore it was clear that asymmetry had been removed, mostly because the developers focused on more important priorities regarding the basic mechanics of the editor. The only two asymmetrical creatures present in the game were Anticipaste and The Grox. An unused cell named "Eyeguy" is also made entirely of asymmetrical parts.
This issue was unexpectedly resolved on the 21st of July when Patch 1.05 was released, allowing players to create asymmetrical creatures by using the A key to drag a single part to the desired location. Asymmetry works for all editors except the building editor, which doesn't use symmetry to begin with.
Before Patch 1.05, some people experimented with creating asymmetrical creatures, like the Grox. While it is obviously possible, the catch is most were unsavable and unusable in the game itself.
However, it was found that it is possible to use and save an asymmetrical creature. As long as it had the characteristics of a symmetrical creature, ergo 2 hands for tools, feet, a mouth, and eyes. The limbs may be completely different, but with 2 the creature could function normally and not cause any glitches in Spore.