After hitting the enemies base, Kang Roo appears as a boss.
For all chapters - Upgrade your Cat Wallet to max level, when enemies will come near your castle, send out few Tank Cats/Wall Cats. In the meantime, wait for your money to go up. When B.B.Bunny appears, start spamming Axe Cats/Brave Cats. At this point, your money should be maxed out. So send out all of your basic cats at once. And that's where Kang Roo comes into a play. Altrough, there's no need to worry. Titan Cat /Mythical Titan Cat will do his job.
another strategy is that kang roo is not good against groups, if you only send macho cat, wall cat and ninja frog cat this stage can easily be beaten and if you sometimes have enough money, a cow cat can speed up the level