The Revenge Shark is a whale shark. It only appears in Super Darius II game.
Granted, given the machine's limitations, perhaps I'm unreasonable, but sadly, the pesky turrets and support ships are all you have to contend with. But pesky is a bit of an understatement, as the turrets and support-ship runaways cannot be taken out. You can, however give Revenge Shark a bloody nose and knock out his fins.
He basically scrolls back and forth. His prow and a few turrets near the conning tower fire pesky bullets of the Battle Garegga type-hard to see. Curiously enough, Revenge Shark also launches a support mech out of nowhere who joins in the carnage, and a second support ship with a biggie beam. The decks keep on sending out the kind of ships you've been eating for breakfast since the start of the game, so they should pose not much of a problem. Apart from the bullets and beams, you should avoid not colliding with him; I'm thinking of the the dorsal and ventral fins here.