Charmed - Episode 622 - It's A Bad, Bad, Bad, Bad World, Parts One and Two

Under the guise of sending Chris back to the future, Gideon (guest star Gildart Jackson) creates a portal that puts Chris and Leo in a mirrored world where evil prevails. Phoebe and Paige travel to the parallel universe to rescue Chris and Leo, only to find themselves in a battle with their evil counterparts. Unable to vanquish one another, both sets of sisters realize that Wyatt is unprotected and in danger from Gideon.
Upon returning to their own world, Phoebe and Paige realize that their world is now too good, and every little infraction is a capital offense. The shift between universes causes Piper's memory to be erased, and Gideon tricks Piper into casting a spell on Phoebe and Paige so that they, too, forget Gideon's evil intentions. With the Charmed sisters under the spell, Leo and Chris are left to stop Gideon from completing his plan. Meanwhile, Piper gives birth to baby Chris.