Successfully complete the indicated task to unlock the corresponding character:

Arnold: Get 30,000 points in Shiverpool 2.
Big Z: Get 100,000 points in Legendary Wave.
Elliot: Get 40,000 points in Pen Gu North 3.
Geek: Get 60,000 points in Pen Gu South 4.
Tank: Get 40,000 points in the Boneyards.
Tatsuhi: Get 15,000 points in Pen Gu South 2.