This stage first spawns one Rain D. and a flow of peons. When the enemy base is damaged to around 400,000 health, a group of four Rain Ds spawn.
Rain D. has a lot of knockbacks, so use easily-stackable heavy-hitting units like Dragon Cat to push him back, defended by a steady stream of meatshields. When the group of Rain Ds appear, use strong, fast area attackers like Paris Cat to keep them away from your base. If you don't have Paris Cat, use Bahamut Cat instead. Use the Cat Cannon when their attacks de-sync so that they all attack at the same time, so you won't have to use as many meatshields.