T - The Flash (2014) - Season 4 Episode 16 - Run, Iris, Run

Team Flash confront a new bus meta, Matthew Kim aka Melting Point. He has the ability to swap people’s DNA, so during a battle with Team Flash, he transfers Barry’s super speed to Iris. Now, with a new threat unleashed on Central City, Barry must act as the team leader while Iris takes on the mantle of superhero speedster in order to defeat their new foe.

Aired: 13 Mar 2018