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 swiped out by the massive HP and DMG 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.