No akuma today, Adrien's sad

Adrien's heartbreak over Ladybug leaves him ideally vulnerable to akumatization... but Shadow Moth is his father, and he won't akumatize his own son like that. When he realizes what he's sensing, he detransforms and has Adrien's bodyguard bring him home immediately so he can (awkwardly attempt to) give his son a comforting talk. His supervillainy normally occupies so much of his time that he barely sees his son, so Plagg immediately notices the difference.

Example of:
Even Evil Has Loved Ones