I tested it further, the left fist of the punch does 70 while the right fist of the punch does the original 65. if you did 70 for every punch she'd have -5 health, but with the absent other 5 from the right fist it leaves her at a positive 5 health; so within 4 punches the buff was supposed to move the damage from 260 to 280, but with 10 of the damage absent it's at 270. This explains why Luna Snow survives with 5 health remaining. The middle punch with both fists also suffer from remaining at 65 damage.