1. Naruto Uzumaki: Known as the strongest user of "Ninjutsu," Naruto's abilities have defeated numerous ninjas. He even persuaded Sasuke Uchiha to return to the Hidden Leaf village using his power of persuasion. Anyone attacked by Naruto's Ninjutsu is in serious danger. 

2. Mei Terumi: As the Fifth Mizukage, Mei possesses powerful bloodline limit abilities including Boil Release and Lava Release. Emitting corrosive gas and molten rock from her mouth, Mei's techniques can penetrate even the strongest opponents' armor. Her formidable mouth abilities may explain her single status.

3. Zabuza Momochi: Dubbed "The Demon of the Hidden Mist," Zabuza is a powerful antagonist.

Despite being injured, he killed several subordinates using only his mouth, even biting off a kunai weapon to defeat enemies. Few ninjas can match Zabuza's exceptional mouth abilities. 

4. Orochimaru: A legendary figure in the series, Orochimaru is known for his extraordinary mouth abilities. In a battle against Hashirama Senju, he bit off a piece of flesh from the Ninja God himself, displaying his daring and powerful abilities. 

5. Jugo: Possessing the dangerous ability called "Cursed Seal," Jugo can absorb chakra from others by biting them, which can be deadly. His incredibly strong mouth abilities may lead to fatal consequences.