Her regular attacks are powerful and inflict Petrify. When she is alone, or only with Mindy, Sandy's Overdrive is Mega-Graviton, which deals 43.75% of all characters maximum HP and is considered magical damage. It causes several status ailments: Doom, Slow, Sleep (for 99 turns), Darkness (for 99 turns) and Silence (for 99 turns).
When she is with Mindy and Cindy, they will use the deadly Delta Attack executed only by Dark Cindy, which always deals 99,999 damage per hit (6 total) and ignores Auto-Life.
Dark Sandy's special move is Razzia that deals 169,710 to 191,631 physical damage, meaning it can be reduced with physical buffs and Def+% auto-abilities. It also removes Auto-Life.
It's best if the entire party can have Accuracy, Agility, Strength, and Defense at 255, and Luck at 120 or higher, with HP of at least 30,000. As long as Sandy is fought alone, she is easy to defeat. If the party has the Auto-Phoenix armor ability, they will not cause much trouble.
When fighting the three Magus Sisters together, to avoid an instant Game Over at the start of battle the Magus Sisters aeon must be summoned, just in case other attacks before Delta Attack kill the aeon before their purpose is served.
As with any other enemy, Dark Sandy can be killed instantly by Yojimbo'sZanmato attack, along with the other Dark Magus Sisters if the player fights more than one of them.