Episode 70 of "Charmed"
s04e04 Enter the Demon
Title: Enter the Demon
Original Air Date: 10/18/2001 on WB
Director: Joel J. Feigenbaum
Writer: Daniel Cerone
Guest Stars: James Hong (Zen Master), Jamison Yang (Shopkeeper), Jeanne Chinn (An Ling), Jacobi Wynne (Mason)
Plot Outline:
While making a potion, Paige accidentally switches bodies with Phoebe. Meanwhile, when an apprentice ninja kills his master, the sisters must find a way to vanquish him, while learning to control their switched powers.