Growing Up (Expert) is the first stage in Adult Cat Awakes!.
Start the level. All that will spawn are Doge Darks in a slow rate.
Later on, another Rain D. will spawn, and more Metal Doges will spawn in groups of two.
Begin the battle. Drop a few Erasers to stall the Doge Darks for a while. When you get to max money, begin to use a few cats. Enough that you get to the base, but not so much that they don't die.
When you attack the base, Prisoner Cat will spawn with a Rain D. Prisoner Cat has very slow movement, but all the other enemies move faster.
Let the Rain D and Metal Doges get close to your base, then use long-Rangers to destroy them. By the time they're all dead, Prisoner Cat should be near the base. Use close-ranged cats like Jamiera, Crazed Titan, and Awakened Bahamut to hit Prisoner Cat. Also spawn meatshields, Island, and Crazed Whale for the Metal Doges.
After a while, the second Rain D. should spawn. Stall with meatshields, and your long-Rangers should be able to hit Rain D while not getting killed by Prisoner Cat.
Once you kill the second Rain D, continue to kill Prisoner Cat with close-Rangers. Eventually, you should win.
Do note that a third Rain D. will also spawn if you take too long.