It's not a coinflip. The most practical use for this card, outside of using it against a known opponent (this could work wonders against Akebono, for instance), is a darkness/light duo with reflective shields, using this as a finisher.
I balanced it by comparing it with PU as a finisher, and with firebolt as a straight damager. Not the most practical comparisons, but they do make me more confident that it's at least close to balanced as is.