Seahorse Siren is the fifth stage in Barking Bay.
This level is just Sir Rel spam. In total, there are 15 waves of Sir Rels with 8 Sir Rels each. The waves spawn around 10, 40, 80, 120 and 160 seconds. After 66.7 seconds, an Oldhorn will come out, and after 100 seconds, Sir Rels independent of the huge waves will begin spawning in 10~20-second intervals.
Strategy 1 (Cheese)
This strategy does require a bit of luck, but the procedure is extremely easy to pull off. Start by sending a Metal Cat to block the 1st Sir Rel (if you have it) and spawn Awakened Bahamut Cat when the 2nd Sir Rel starts hitting your base. After that, spam your meatshields and Manic Lion Cat. Try to summon Metal Cat, too. If done correctly, Awakened Bahamut should destroy the base while your meatshields prevent Sir Rels from hitting him.