Grausam

Grausam, also known as the Miraculous Grausam, was one of the Seven Sages of Destruction that served the Demon King. Along with the other Sages and the Omniscient Schlacht, he battled the Hero of the South.

[Spoiler] Grausam possesses incomparably strong mental magic that able to remove portions of someone's memory using his magic. Grausam is able to trap others in an illusion that can show his victim the dream which they already abandoned and accepted that it would never come true. The mental magic is powerful enough to make the illusion imperceptible with reality and even deceive the eyes of great demons. Hi is able to alter his face and form, blending in the society of any era. [/Spoiler]

(Source: Frieren: Beyond Journey's End Wiki)