Reeva was not in a good position. He only retained a basic instinct of his in this full demon mode and he only does things that he himself would consider fun. Which means he could go off the rains if intrusive thoughts were more powerful.
Moreover, His real self couldn't possibly be controlled since he had plenty of joy to go around.
After seeing her futile effort to hurt Reeva, the mother looked for a new target. After fighting humans for such a long time she knew the best trick she could use against a power like Reeva.
The vines shot off the snow again but this time it wasn't targeting Reeva but the people that were still alive, albeit incapacitated by pain. The people had no power to stop such vines but Reeva had.
