The mysterious 9th stance, the qi-breaking stance, which can be used to deal with opponents with advanced inner power. FQY taught LHC the verbal formula and training method, then it was never heard from again.
Thinking about it though, why would LHC ever need to use it? If someone attacks him with a powerful qi-backed fist, he uses the palm-breaking stance; if someone attacks with with a powerful qi-backed sword strike, he uses the sword-breaking stance, and so on. If someone just stands there with diamond body or the like... well, then just stab him, since even monsters like Xuzhu are unable to effectively take a dagger with their inner strength alone. And on the off-chance that someone can... then just stab him in the eye.
So, what is the point of the 9th stance? It is not useful in defending against vocal attacks (which LHC has been shown to be vulnerable to), since the quickest way to shut the attacker up would simply be to stab him with one of the other stances first. LHC, while completely unable to employ any inner power of his own, was able to counter the weapons and unarmed strikes of experts employing considerable inner power using just the first 8 stances with little difficulty. All in all, the 9th stance seems rather pointless...