Bai Long only needed to roughly possess around 50% cultivation in the Qi Child Realm to be able to use the technique he needed to obtain control over Meirong.
Unlike the others whom he turned into Yin Puppets whenever he wanted to control then, Meirong was someone who had a cultivation higher than him and impossible to get close enough to attach a Yin Puppet Talisman even if they manage to get her sense of existence shook.
Due to this Bai Long was forced to choose another technique which could allow him to take control over Meirong.
The Demon's Curse.
This technique wasn't an absolute technique like the Yin Puppet one which allowed him to turn the ones he targeted into mindless corpses who followed his order and were completely under his control.
Instead, it was more like a restriction which forced the one under Bai Long's control to do as he ordered them to.