Meref tried to increase the emotion of forgiveness and guilt. It was even easier than trying to control someone's mind, he just needed to intensify each emotion and get Theo to stop controlling his people.
If that worked, the chances of him winning would increase, he could use his people to attack together, and then when Theo was exhausted, it would be the time for his death. It was a good plan, Meref thought it was his chance. He saw that Theo was falling into his plan, however, he did not imagine that his mind was more powerful than he thought and managed to return to normal in less than 1 minute.
He couldn't even get Theo to think he was being too excessive, at most he made him reflect on his actions, but it wasn't enough, he was weak... His mind was weak compared to Theo's. Now, he was even more afraid. A powerful mind that managed to control many people at the same time, and still managed to protect itself, was scary!
