The user can redirect any cause to any effect, undo anything by inverting the relation cause/effect, or separate them entirely, making a specific effect impossible to be caused or a specific cause not producing any effect.
This allows one to achieve virtually anything by redirecting the selected cause to the desired effect. A finger snap which normally causes sound and kinetic force could instead cause a sun explosion or massive resurrections.
The ability has two categories of applications : active and passive. Active applications consist in manipulating causality "on the fly," adapting it to the momentary needs of every situation. For example, the user could instantly erase anything from existence, by making its existence the cause of its own nonexistence. Another possibility is the instant rewriting of a whole reality, by making Reality X (present) the cause of Reality Y (desired).
On the other hand, passive applications consist in creating causal networks that work permanently (or until the user changes it) and independently from the user (excellent for defensive purpose). One of the most striking examples is Absolute Immortality : by making alterations to his/her being the cause of its restoration, the user will automatically, instantly, and indefinitely recover from anything - even if his entire existence has been completely wiped-out.
At the top level, the user would be able to rewrite the law of causality as a whole, essentially playing God.