The Battle Cats - Heavenly Tower [Floor 1-10]
One of the best additions to the game. You get a reward each floor you clear and even a rare ticket on 10F.
1-9F are super simple.
10F has some monthly event enemies. If you don't have A. Bahamut, try to get a large stack of long ranged attckers. If you have A. Bahamut, he can quickly eliminate Martin or the Celeboodle and the rest of your long ranged attackers can handle the rest of the enemies.