Supergirl 4×04 “Ahimsa” Season 4 Episode 4 Sneak Peek – J’ONN MEETS MANCHESTER BLACK — When Supergirl (Melissa Benoist) needs help, Alex (Chyler Leigh) asks Lena (Katie McGrath) and Brainiac (Jesse Rath) to team up. Meanwhile, J’onn (David Haredwood) questions his decision to quit the DEO. However, after running into Manchester Black (guest star David Ajala), he realizes there are a lot of ways to help his fellow aliens during this tumultuous time. Armen V. Kevorkian directed the episode with story by Eric Carrasco and teleplay by Katie Rose Rogers & Jess Kardos (#404). Original airdate 11/4/2018.