Supernatural (TV series)/Recap/S02/E05 Simon Said

Season 2, Episode 5:

Simon Said
Sam has another premonition, this time of someone committing a murder-suicide, so he and Dean investigate and discover that more of "Yellow-Eyes' children" are involved: young people who, as children, were fed blood by the Yellow-Eyed Demon and have subsequently developed supernatural powers. Their first suspect is a young man whose biological mother was the first victim, but they learn that the man's long-lost twin brother was responsible and is taking revenge for being separated from his brother. To save Sam and Dean, the man kills his brother.

Tropes

 * Charm Person: Andy and his twin.
 * Evil Twin