Parasite Demons

The Parasite Demons, known as Leech and Suck, were once powerful demons who were cursed by a witch many centuries ago, leaving them severely weakened. In order to survive, they had to absorb the magic of other magical beings. Their loss of power also caused them to become social outcasts in the demonic world. The Parasite Demons enjoyed targeting witches for revenge but ultimately searched for a source of magic that would restore them to their former power.

History
The Parasite Demons hired a Hawker Demon to kidnap the newborn Wyatt Halliwell, as they sensed his power would be enough to restore theirs to full force. The Crone tried to warn the Hawker of the danger, but the Parasites forced him to try again. After the Hawker Demon was vanquished he left a knife behind, which Paige traced back to the Demonic Market.

Paige entered the market undercover, and attempted to vanquish the Parasite Demons, but was defeated and captured by them, who began to drain her magic. When Phoebe received a premonition of Paige in danger, she and Piper went to the market, at which point the Parasite Demons realize that nobody is left at the manor to protect the baby.

However, Leo fought to protect Wyatt, giving the sisters enough time to return to the manor. Piper then blew up Leech, while Suck escaped. However, back at the market, the Crone vanquished him for trying to take the child and causing chaos at the market.

Season 3
Ignatius resurrects the Parasite Demons in What Hurts the Most, in order to keep the Destined One's busy while he fulfills his plan.

Notes and Trivia

 * The Parasite Demons had an albino-like appearance, possibly a side-effect of the curse.
 * Both demons were killed with molecular powers the first time.