The Super Juggernaut is found in the upper levels of Survival Mode. It is very hard to find and cannot be acquired in regular modes. It also appears to be bigger than the regular juggernaut. It appears to be 2x larger than a regular juggernaut and has better statistics than the regular version.
Since Juggernaut is a word to describe "a huge, powerful, and overwhelming force", they are often depicted as giants in popular media, such as the Marvel Supervillain Juggernaut. These Super Juggernauts fit well to the commonly construed image if a juggernaut, even more so than the regular Juggernauts.