S6, E11: Supergirl and team must stop Nyxly 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 visits her mother’s birthplace in Ireland, eager to dig into her past but is shocked by the small town’s icy reception towards her.