Flooded Cave is the seventh stage in Squishy Cave.
If you don't have any anti-black characters, Beware the Shadow Boxer K and Gory Black, as they can push your lines far enough for the doge darks to hit your base.
Use long range cats such as Sexy Legs and Dragon Cat, along with Wall and Macho Cat to stall the blacks. Continue spawning the mentioned cats throughout the level. If you have any anti-black ubers, those can help too.