Mural of the Devil is the third stage in Squishy Cave.
A few Mooths and Squire Rels will spawn once the battle starts. More Mooths will spawn for you to max out your Cat Wallet, and less than 15 seconds in, J.K Bun Bun will spawn along with a moderate flow of Mooths.
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 like island cat (fish cat true form), Anti-Floating, or long ranged attackers.
Also, you don’t need to be scared of the mooths, they’re only at a 100% magnification, so they’re really easy to beat.