S4, E16: Team Flash confront a new bus meta, Matthew AKA Melting Pot (guest star LEONARDO NAM), who has the ability to swap people's DNA. During a battle with Team Flash, Matthew accidentally takes Barry's speed away and gives it 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 Super Hero speedster in order to defeat their new foe.