An Elemental Ki Strike enhancement
Water Ki Melee Attack: You have learned several joint strikes. You can attack these weak points of your opponent, throwing them off balance for a short period of time. This reduces their armor class by 2, applies a -10 penalty to their Balance skill, and renders them vulnerable to sneak attacks. A successful Reflex save negates this effect (DC 10 + Half Monk Level + Wisdom modifier + Trip modifiers). The target receives periodic saves to attempt to break free of this effect. Works against bosses.
The Unbalancing Strike is a Way of Water attack that can be used as part of a finishing move.
Only one Elemental Ki Strike may be chosen per class tree but do not appear to be exclusive. If you unlock the ability in another class tree, you should be able to choose another attack type.