Mural of the Devil is the third stage in Squishy Cave.
A strategy to beat this level is to spam Tank Cat, Macho Cat and any other meatshields just before the boss is released. Try to build up a high amount of long ranged attackers such as Dragon, Sexy Legs and Bahamut, and make sure you keep the spam up, otherwise J.K Bun Bun will kill all of your attackers.
Dancing Flasher Cat is very helpful in this stage. It can do massive damage each shot and it can also slow Red Enemies. Bahamut is essential. You could also do with some Anti-Red, Anti-Floating, or long ranged attackers.