Rotter is a 2010-introduced and cartoon-only character. He is a phantom and a teacher at Monster High, having been a student there in his younger days. He officially teaches Dead Languages, but also at times Ge-ogre-aphy and Physical Deaducation. Rotter is a driven teacher who has high standards for his students to meet, to the point that acquiring an 'A' in his class is an impossibility.
Mr. Rotter believes in order and has little patience for students that try to cause chaos. He is, however, not a strict teacher and enjoys to spark enthusiasm for both his classes and the other ones in the students. This means that sometimes Rotter fails to understand when students are not enthusiastic about some of the classes. He is known for never giving 'A's.
Rotter has grey-to-green skin and sandy hair. He is usually dressed in a brown coat.
- December 16, 2010: Rotter makes his 2D cartoon debut in "Idol Threat".
- February 12, 2012: Rotter makes his 3D cartoon debut in "Why Do Ghouls Fall in Love?".
- Late May, 2013: Rotter makes his diary debut in Lagoona's 13 Wishes diary.
- Rotter is designed after Lon Chaney's 1925 iteration of the Phantom of the Opera, though the Phantom is a separate character.