Evil Magnification Tonic

The Evil Magnification Tonic also called The Prenatal Tonic or The Seer's Tonic, was a tonic originally brewed by The Seer to strengthen the Evil in Phoebe while simultaneously and weakening the Good. The Oracle later used this tonic on Prue Halliwell, in hopes of swaying her towards Evil

The Seer
The Seer began giving the tonic to Phoebe she and Cole became the rules of the Underworld. However, Phoebe hated the taste of the tonic and eventually poured one glass into a potted plant. When the plant died, the Seer admitted the true purpose of the tonic - to strengthen the Evil in her and her unborn baby and weaken the Good. Because of this, Phoebe became weak and the baby became stronger.