Watch Supergirl Season 3 Episode 20 Online. Best and Free Online streaming for Supergirl TV Show. We picked the best sites to stream s03e20. Simply pick a site below and click "Watch Now!" button next to it. Some of the links may be broken, please upvote the working and good links so other users see those links for Supergirl Season 3 Episode 20 s03e20 at the top of the list.