When Lianwu was teaching Xiao Xue the Spirit Control Technique, Su Yu went to observe a few times. Among them, there was a kind of spirit talisman called the Shadowless Butterfly. It's a talisman that transforms into an invisible butterfly, allowing it to freely penetrate another's barrier within the same cultivation level to detect whether there is a fight inside the barrier. If there is a strong clash of cultivation inside the barrier, the Shadowless Butterfly will dissipate, which indicates that the situation inside is very dangerous. However, if there is no collision of cultivation, the Shadowless Butterfly will remain intact.
This is a very simple spirit talisman used to test situations. Su Yu found it interesting at the time, so he learned this technique.
