(someone) up to monkey tricks

Translations
(кто-то) занимается мошенничеством
We caught him up to monkey tricks, trying to change his grade.
Мы поймали его на мошенничестве, пытающегося изменить свою оценку.
Definitions
The phrase '(someone) up to monkey tricks' means that a person is behaving mischievously, playfully causing trouble, or engaging in sneaky or naughty activities, often in a lighthearted or humorous way.
Words
monkey

noun
обезьяна
trick

noun
трюк