Akademik

иду на вы
• ИДУ НА ВЫ obs, now coll, often humor
[sent; Invar; fixed WO]
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⇒ I am going to attack you (in contemp. usage, I intend to oppose you, argue against your point of view etc):
- I come against ye!
     ♦ Бородавкин вспомнил, что великий князь Святослав Игоревич, прежде нежели побеждать врагов, всегда посылал сказать: иду на вы! - и, руководствуясь этим примером, командировал своего ординарца к стрельцам с таким же приветствием (Салтыков-Щедрин 1). Wartkin remembered that Grand Prince Svyatoslav Igorevich, before conquering his enemies, always sent ahead to say, "I come against ye!" Guided by this example, he dispatched his orderly to the musketeers with the same greeting (1a).
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← According to Russian chroniclers, this phrase was used by Prince Svyatoslav (10th cent.) as a declaration of war. In old Russian, the pronoun "вы" had two forms of the accusative case: the full form "васъ" and the short, or enclitic, form "вы".

Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. . 2004.