Red Tuna Coast is the first stage in Sea of Tuna.
The Enemy's Castle will spawn the Boss (Dark Emperor Nyandam)
During the Battle
Using anti-red cats and meatshields such as Wall Cat and Macho Cat can definitively make this level easier. If you have Pirate Cat, this level is very easy. With proper meatshielding, a good stack of them can completely take Dark Emperor Nyandam out of the game, constantly knocking him back when he's about to attack.