At the start, Snaches, Those Guys, some Squire Rel, a Kang Roo and a pair of Otta-smack-u will spawn. When the base will be damaged enough, Gentleman Bros. will come out. After a bit of time, Shadow Boxer K and Dark Otter will appear, and will keep appearing for the remaining of the stage.
Meatshielding is useless, if not for the S.B.K. and the Dark Otters. Island, Crazed Fish and Jamiera are...Well, if you don't use them, you're going to have an awful experience. Bahamut is a win/lose. You never know if he's going to attack in time. Consider also, he gets knocked back easily, so it's extremely dangerous to use him.
In fact, Gentleman Bros. attacks in a pretty slow rate, this leaves you S.B.K.s and Dark Otters as main threat. Bring some meatshield to stop Gentleman Bros. Then spam cats that do good and area damage to kill the dark enemy. Having (Crazed) UFO Cats, Jamiera Cats (Crazed Titan Cat) and Dancing Flasher Cats will help you plenty. Since the dark enemy has been killed, take the break to damage Gentleman Bros. Bring any Uber rare cats or cats with long range (longer than 500) you have!