According to the Star Wars Legends continuity, Palpatine killed Plagueis by using his dark side powers to manipulate the Force and create a powerful storm that struck Plagueis with lightning, which ultimately killed him. However, it is also implied that Palpatine may have used other means, such as poison or physical force, to ensure Plagueis' demise. In the current Disney canon, the exact details of Plagueis' death are unknown and have not been officially revealed.
