A lot of Gories will be spawned after your cats hit the enemy base. They will act as a support to Mooth, the stage's boss.
For all Chapters - When the battle begins, start upgrading your Worker Cat to max level. When the enemies get close to the Cat Base, send out a few Wall Cats. Don't get scared when Squire Rel appears, as she can easily be killed by the Cat Cannon or meatshields. Eventually your money will be maxed out; that's when you can send out all of your Normal Cats at once. When they start to hit the enemy's base, start spawning Sexy Legs Cats and UFO Cats. This will be enough to kill all of those Gories. Now for the main problem: Mooth. All those dead Gories will give you a lot of money. Spend that money wisely by deploying Dragon Cats and Titan Cats and you should be able to win.