Blue Moon Beasts

When the Blue Moon appeared over San Francisco three times which only occurs once every fifty years it affected the Charmed Ones powers making them unstable and giving Phoebe violent and painful nightmares. When the moon appeared in the sky they turned into wild werewolf-like Beasts who attacked whitelighters and Elders partly because of their strained relationship concerning Leo and because they felt threatened by them.

The Elders planned to assign a new whitelighter to the Charmed Ones since they suspected (correctly) that Leo was the one who killed Zola however they also felt that Leo was a threat to the sisters. When Leo confronts the new whitelighter Danny, he suggests that he souldn't take on the duty. Moments after Leo left, the new whitelighter was mauled by three savage beasts.

When the Elders discover him attacked they immediately suspect Leo however the Charmed set a trap with the crystal cage for the beasts with another whitelighter named Marcus as bait. Waiting for the beasts as the blue moon rises the Charmed Ones suddenly turn into the beasts and attack the whitelighter. With his last ounce of strength before passing out, Marcus traps the sisters in the cage. The Charmed Ones wake up the next day inside the cage next Marcus' body realising that Phoebe's dreams were real and that they were really the creatures suspecting that the Blue Moon caused this to happen.

During the final night of the blue moon the sisters were preparing to cage themselves when Leo (being possessed by a Possessor Demon) attacks them and goes after the Elders. The Charmed Ones expel the demon out of Leo however the Elders not realising transport him to another location. When the sisters protest the blue moon rises and they attack the Elders who had to defend themselves and knock them out. The sisters try to find the demon that possessed Leo and when the Odin, one of the Elders say no because they turned into monsters they tell him that it was only the Blue Moon that caused the change and it wouldn't happen again for another fifty years making the Charmed Ones in their 70-80's.

Powers & Abilities
As the beasts, the Charmed Ones displayed animalistic Super strength and agility similar to how Piper transformed into a Wendigo. Their attacks must have been enchanted since normally a whitelighter cannot be hurt by anything except a Darklighter arrow and it took a group of Elders to try and heal Marcus and Danny.

Appearances
The Charmed Ones became the beasts in a total of 1 episodes throughout the series

Season 7

Once In A Blue Moon