Hundreds of witches, including the Charmed Ones
A peaceful gathering for witches
In January 1967, Penny and Allen Halliwell planned to hold a "magical be-in" at the manor. They invited hundreds of their witch friends to come tap into the power of the Nexus and, as Penny put it, "ride the magic wave."
A warlock named Nigel got wind of these plans, and saw an opportunity to massacre a large number of San Francisco's witches. He sent his girlfriend Robin, an evil witch, to ingratiate herself with Penny.
On the night of the be-in, Penny suspected that evil covens might try to crash the party, and had everyone set up crystals around the manor to ward off evil. Robin used this as an excuse to slip into the attic and chant a spell to unleash evil in the manor before the crystals could take hold. Unknown to her, Allen, who had suspected she'd been acting funny, walked in on her in the middle of the chant. Robin killed him with a fireball. Penny heard the commotion and killed Robin on the spot. Out of concern for her friends' safety, she cancelled the be-in.
The Magical Be-In is very much like the Human Be-In.