Popsugar Entertainment Siren Siren TV Show Cast Prepare to Be Enchanted by the Cast of Freeform's New Mermaid Series, Siren 29 March 2018 by Terry Carter View On One Page Photo 3 of 6 ADVERTISEMENT () Start Slideshow Share This Link Copy ← Use Arrow Keys → 3 Sibongile Mlambo as Donna Former Teen Wolf star Mlambo plays Donna, a mermaid who is captured in the premiere episode by a local fishermen. Previous Next Start Slideshow SirenTV