Many Halo players use Forge to do various things, like make a new map, or switch a few weapons around. Some people even make "forge-art," which is basically a design created with various objects found in Forge. Most forge art is cool, but often random. This particular *image is considered forge-art; a sculpture of a giant iguana. Like I said, cool, but random...
*I did not make this, the author is actually OMGxRob.