Got the medium badge on my 4th try. After a while, his health will stop dropping. At that point, you have to keep dodging until he withdraws the pearl. He will then explode. Simple as that.
A= Save/Help everyone ( keep the sharks away until girl gone on plane with tentacles)B = Save/Help everyone except for stranded girl C = Die from boat dropping mines D = Die from submarine E = Kill everything and Everyone
 "Ultimate Crab Battle"){kind=icon}
 "Epic Combo!"){kind=icon}
 "The Company of Myself"){kind=icon}
 "The Majesty of Colors"){kind=icon}