3. Yamato Hotsuin, Shin Megami Tensei: Devil Survivor 2
There are two different battles against this guy dependent on the route you take. In one battle, you fight Yamato and 5 other groups of demons. When you kill one group, he gets more turns. When all enemies are defeated, he can move so many times that he can actually kill all four of the players groups in a few turns. He can even kill a max level character equipped with max level demons that have the capability to heal after every turn. Yamato himself can attack from multiple tiles away, restore his MP continuously, and revive his own demons at the beginning of every turn. He also has an unblockable magic attack that he can use twice and reflects all physical attacks. For the second battle, he employs a magic circle that damages both HP and MP. All of the demons can be revived by a Norn. Yamato himself has the strongest magic attack in the game, along with Drain, which damages a character or demons HP and MP and heals his HP and MP, and Prayer, which fully heals HP and gets rid of any ailments. With his demons, he can prevent you from healing and attack two separate times. He also has an ability that increases magic damage by 50%, but doubles MP costs. This is offset by Drain.