She is a mermaid-like creature with a saint innate body. Just like the Fuxi and other accient godly creature, her race had their bloodline sealed. When she first met Zhong Yue he helps her unsealed her bloodline making her able to walk for the first time in her entire life. Even without legs, Yin Fanxuan was renown for being undefeated at the deity level, even Zhong Yue was not her match. This stay the same when they both became Hevanly gods, Zhong Yue still was not her match.
Because she is the rarest of the rarest natural-born Innate Saint Spirit Body.
After Zhong unseals her bloodline, he was tricked and forceed to married Yin Fanxuan in a drunken state without his awareness, the following day he found himself next to a tied up Yin Fanxuan in his bed.