Harpie Lady Phoenix Formation

"During the turn you activate this card, you cannot Special Summon monsters from your Deck or Extra Deck, and you cannot conduct your Battle Phase" is not treated as an effect. (It is a condition for activation.)

This effect targets monsters in your opponent's Monster Zone. You must target as many monsters in your opponent's Monster Zone as possible, up to the total number of face-up "Harpie Lady" and "Harpie Lady Sisters" you control. (Basically, you activate this by targeting 3 or more of your opponent's monsters, but if your opponent only has 2 monsters in their Monster Zone, you will activate it by targeting those 2.)

The process of "destroy the targeted monsters" and the process of "inflict damage to your opponent equal to the highest original ATK among those destroyed monsters" are treated as occurring simultaneously.

The process of "inflict damage to your opponent equal to the highest original ATK among those destroyed monsters" inflicts damage to your opponent equal to the original ATK listed on the card of the 1 monster among those destroyed by this effect that has the highest original ATK. (Even if the original ATK has been changed on the field, the damage inflicted does not change.)