Return to your hand any number of Light Side units in one arena the total build cost of which is 7 or less. Choose any number of your opponent's Dark units in the same arena. Return those units to your opponent's hand if their total build cost is equal to or less than the total build cost of your returned units.
Text Erratum
"Total build cost" in the game text is the sum of all the total build costs of units (including stacked costs) that are returned to your hand.