User blog comment:IamJakuhoRaikoben/Mirajane & Lisanna vs. Azuma (anime)/@comment-72.66.31.250-20111125035748

The evil explosion thing is probably a function of them trying to name her generic energy blasts, and generic things like "throw river at Fried". It's probably easier to assume that rather than there being a water version and a darkness version, there's just the darkness version and the first time she used it she happened to be throwing the river at Fried at the same time for additional punch.