Enamel

Enamel (エナメル質, Enameru-shitsu) was a Mysterious Being that was killed by Metal Bat before he became an S-Class hero.

Appearance
Enamel looks like a giant tooth with his name as a tattoo on his body.

Volume 11 Extra
He is seen lying dead after being killed by metal bat.

Abilities & Powers
While it is unknown now strong he was the fact metal bat went from a C-Class hero to a S-Class hero implies he is quite powerful.