As said above, IT IS CRUCIAL to rush this stage. By using cats with anti-red abilities (Island Cat, Crazed Whale and Bath Cat) and fast cats (Crazed Giraffe Cat), you can beat the stage before the Assassin Bears appear. Do not try to kill them with the Cat Cannon; they are buffed. Well, that is, unless your charge is at an overwhelming number...
Strangely enough, when the player's Cat Cannon Power is upgraded to max level, it can kill the Assassin Bears.
An almost insultingly easy strategy is to simply fill your first rank with Crazed Cats in unevolved form (granting an initial $1000 via Cat Combo), and place Awakened Bahamut in the second rank. Begin the stage, wait for your money to reach $4500 and push the instant win button.