J.K Bun Bun appears as a boss alongside One Horn.
This level tests your ability to spawn meatshields and keep them in front. Otherwise, your units may be wiped out by the massive HP and damage of J.K Bun Bun.
Spawn in Macho Cat and Wall Cat to hold back the lesser enemies that spawn in while you save up your money. Do not attack the enemy base for a while, as when you attack the base, J.K Bun Bun will be spawned. Once you have a max-level Worker Cat and your wallet is as full as it can get, summon in every strong anti-Floating or anti-Red cat that you have. cats like Pirate Cat, Shaman Cat and Bahamut Cat are very helpful here. As soon as J.K Bun Bun is in battle, continue to deploy every cat you have along with Macho Cat and Wall Cat. This should hold him off and kill him off when cats like Bahamut deal damage to him. Due to his high health, he may be a very difficult enemy to fight and the battle may last for a long time, but it is possible.
I just use this army against J.K Bun Bun: Samba, Wall, Monk (or Fisherman), Shaman, Swordsman, Bath, Dragon, Valkyrie, Bahamut, and Sodom. You could substitute Sodom for any other Uber Rares if it is anti-Red/Floating or use Pirate Cat.
For me, I just used Macho Cat, Crazed Cat, Samba Cat, and Wall Cat for meatshields, and Paris Cat, Dragon Cat, True Valkyrie Cat, and Crazed Bahamut Cat for offense. First start off with some meatshields. Upgrade your wallet to max, and start sending everything starting with bahamut, Paris, and meatshields. It should work if done properly, and kill one horns for money.
I used Mohawk Cat, Wall Cat, Dark Cat, Thor Cat, Phantom Thief Cat, Island Cat, Date Masamune (or another uber that can knockback reds and/or floating) and Bahamut. Start out the battle by spawning a couple of Wall Cats alongside with some Thief Cats. They should be strong enough to take down Those Guys along with the Pigges. Max out your Worker Cat level with the cash. When Phantom Thief Cat and Wall Cat start hitting the base, send out Dark and Thor Cats with an occasional Island Cat. Do not panic when JK Bun Bun spawns and starts killing your cats, just stop spawning only Island Cats and save enough money for your red-killer. JK Bun Bun should be near the halfway mark of the stage when you summon out your red killer. Just spam Mohawk, Dark, Thor until you kill him.
This strategy abuses Dread Pirate Catley.
All you need to do is spam some meatshields (all I used was Jiangshi Cat) together with Dread Pirate Catley. Dread Pirate Catley will keep knocking back the red enemies and Jiangshi can easily deal with the non-red peons. To make things easier, you can also bring Crazed Bahamut Cat (Awakened version not recommended), Ururun Cat, and Dark Emperor Catdam for more damage.
This is doable without any combos, but they will make things easier.