Starpedo is one of Starfy's forms that he gets from Bunston. It can be obtained in Chillydip Cove (world 3 level 3). It resembles a seal with a tail fin made of ice that can change into the Icy Spike for a very short amount of time.
You can find the Icy Spike upgrade in Sogwood Forest, the Ice spike will enable you to go against faster moving currents. there are special blocks only Starpedo can hit that creates rings that only Starpedo can swim through but there is a time limit. If you take to long the ring jumping "game" will end. But it is possible to hit the block again to redo the game. Winning will gain you around 25 pearls. Once you win the hoop game, it isn't possible to redo it unless you leave or finish the level and come back to the block. It occasionally makes a *kwee* sound.
The soft ice that seems to be goo, occasionally found in Chillydip Cove, can only be destroyed by Starpedo's Icy Spike.