Sigma Drago is assumed to be a DarknessX evolution of Omega Drago in primal stage and is believed to once have entered X stage.
Omega Drago one day got sick and began to do evil deeds without knowing. Soon his colors changed to an inverted style. Storm Skyress appeared on Earth to take him on when he began to cause destruction in the brawlers and Kyles town. Skyress and Kyle became brawler and guardian momentarily when they discovered that a defect in Omega Dragos cloning process caused a strange transformation that happened randomly. The symptom was that he would get sick then become a darkus and pyrus while getting possessed by the last holder of the silent core. This meant that Naga now had control over Omega Drago who was now dubbed Sigma Drago. Through the combined efforts of the brawlers,Storm Skyress,and Kyle Sigma Drago was changed back and Nagas spirit was eliminated.
The scientists of the Bakugan Cloning Project believe that during the cloning process there may have somehow been exposure to something related to DarknessX due to similar evolution energy readings. This is also believed due to the fact that he seems to act like he is in an uncontrolable form of the primal stage of bakugan evolved in the Darkness X project.
Sigma Drago has an inverted color scheme of Omega Drago and is believed to have varied Gs. His first appearence he had 950 Gs. In his second he had 1000 Gs. In his third and final appearence he had 2000 Gs. In his current status being a non ability aided controlled transformation he is at 1450 Gs and can destroy one ability during a brawl and it can't be used for the rest of the brawl.
He has the inverted color scheme of Omega Drago as I have already stated. The appearence of Sigma Drago in his first two appearences is in the images. The top 1 is his first and the bottom one is his second.