This form of Lord Cobra is way more advanced than he was in Madagascar, Camelot, or even what he would've looked like if the Villain League successfully obtained Kairi's Blood. He stands on 2 of his freaky heads like actual legs while the other two stick up in the air. this result with him looking almost raptor and/or dinosaur-like. this was actselly all part of both Malefor and Master Xehanort's plan, to better Lord Cobra even more then he already was, and Mirage (and maybe Fagin before No-Face got a hold of him) were part of it. However, after the big battle, Giga Cobra was short-lived and he turns back into normal Cobra after a huge and massive defeat, ending with the usual angry rant of venegence from Mang.
MSM didn't use Spore to make this Lord Cobra form because he was afraid Scroopfan would be PO'ed like last time when MSM tried to use his own Spore to build a duplicate Lord Cobra, nearly causing him to be kicked off of the series.