A supergiant is a very large Giant. It is locked inside the Desert statue until the statue dies. When this happens, instead of winning, you will have to kill this supergiant. It has a very large amount of HP, much more than a normal giant, so you will need a lot of Swordwrath and Speartons to defeat this supergiant. And use giants
You can also use the same stratgy for giants with a Spearton just get alot of archerdons and you should kill the super giant with ease. Note: attempt to stay under its legs and just go the oppisite direction (s)he is attacking.
In Stick War: Legacy, after you almost destroy the statue in Last Stand, the Supergiant emerges, but the moon in the background suddenly shines brightly and a Giant, bigger than the Supergiant arrives and kills the Supergiant. If you have powerups at this point, you should use them.