Supergirl (Melissa Benoist) and team must stop Nyxly (Peta Sergeant) from vanquishing a familiar face from Supergirl's past - Mr. Mxyzptlk (guest star Thomas Lennon). Mxy returns and explains Nyxly's dark history to the super team in the best way he knows how - in song form. Meanwhile, Lena (Katie McGrath) visits her mother's birthplace in Newfoundland, eager to dig into her past but is shocked by the small town's icy reception towards her.