Originally Posted by david0925

Then you will read that Mimiron explicitly say something along the lines of "Sorry friends, I was MC-ed by Yogg-Saron. Thanks for freeing me and I'll help you." You may have been too happy beating this encounter to pay attention to the dialogue, which is 100% understandable, but the dialogue is there to prove that he was influenced by Y-S.

You can also tell that he was either sarcastic and/or insane when he called you friend in that tone at the beginning of phase 1