A series of stills from "Lost Souls," the upcoming fourth episode of Supergirl Season 6, mark the debut of actor Peta Sergeant as the character Nyxly.

"Lost Souls" is set to air on The CW on Tuesday, April 20 -- one week after this coming Tuesday's episode, "Phantom Menaces." It was recently revealed that Sergeant had joined Supergirl's sixth and final season as Nyxly (known in the comics as Nyxlygsptlnz/Mrs. Nyxly, Mister Mxyzptlk's partner). In addition to Sergeant's Nyxly, the photos from "Lost Souls" feature the likes of Zor-El (Jason Behr), Sentinal (Chyler Leigh), Brainiac-5 (Jesse Rath), J'onn J'onzz (David Harewood), M'gann M'orzz (Sharon Leal), Lena Luthor (Katie McGrath), Dreamer (Nicole Maines) and, of course, Supergirl (Melissa Benoist) herself.

RELATED: Thomas Patrick Lennon Announces Mr. Mxyzptlk's Supergirl Return

Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0001r.jpg -- Pictured: Peta Sergeant as Nyxly, Melissa Benoist as Supergirl and Jason Behr as Zor-El Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0002r.jpg -- Pictured: Melissa Benoist as Supergirl and Jason Behr as Zor-El. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0003r.jpg -- Pictured: Chyler Leigh as Sentinal, Jesse Rath as Brainiac-5 and David Harewood as J’onn J’onzz. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0004r.jpg -- Pictured: Sharon Leal as M’gann M’orzz and David Harewood as J’onn J’onzz. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0005r.jpg -- Pictured: Chyler Leigh as Sentinal and Katie McGrath as Lena Luthor Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0006r.jpg -- Pictured: Nicole Maines as Dreamer, Jesse Rath as Brainiac-5 and Sharon Leal as M’gann M’orzz. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0007r.jpg -- Pictured: Nicole Maines as Dreamer and Jesse Rath as Brainiac-5. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0008r.jpg -- Pictured: Jason Behr as Zor-El. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0009r.jpg -- Pictured: Melissa Benoist as Supergirl, Jason Behr as Zor-El/Man and Peta Sergeant as Nyxly. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0010r.jpg -- Pictured: Peta Sergeant as Nyxly and Melissa Benoist as Supergirl. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0011r.jpg -- Pictured: David Harewood as J’onn J’onzz, Sharon Leal as M’gann M’orzz, Katie McGrath as Lena Luthor and Nicole Maines as Dreamer. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0012r.jpg -- Pictured: Katie McGrath as Lena Luthor, Nicole Maines as Dreamer, Jesse Rath as Brainiac-5, Sharon Leal as M’gann M’orzz, Chyler Leigh as Sentinal and David Harewood as J’onn J’onzz. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0013r.jpg -- Pictured: Jesse Rath as Brainiac-5 and David Harewood as J’onn J’onzz. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0014r.jpg -- Pictured: Melissa Benoist as Supergirl and Peta Sergeant as Nyxly . Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.
Supergirl -- “Lost Souls” -- Image Number: SPG604fg_0015r.jpg -- Pictured: Melissa Benoist as Supergirl. Photo: The CW -- © 2021 The CW Network, LLC. All Rights Reserved.

Per the full official synopsis for "Lost Souls,"

SUPERGIRL FINDS A WAY HOME -- Supergirl (Melissa Benoist) finds an opportunity to escape from the Phantom Zone but it comes with some dangerous strings attached. Meanwhile, Lena (Katie McGrath) joins the Super Friends on a mission but finds she disagrees with their plan of action against the Phantoms and wonders if she is truly ready to be a part of the team. Alysse Leite-Rogers directed the episode written by Karen E. Maser & Nicki Holcomb (#604). Original airdate 4/20/2021.

Supergirl stars Melissa Benoist as Kara Danvers, David Harewood as Martian Manhunter, Chyler Leigh as Alex Danvers, Nicole Maines as Dreamer, Jesse Rath as Brainiac-5, Azie Tesfai as Kelly Olsen, Julie Gonzalo as Andrea Rojas and Staz Nair as William Dey. New episodes premiere Tuesdays at 9 p.m. ET/PT on The CW.

KEEP READING: Supergirl Is Stuck In the Phantom Zone in Latest Promo Spot

Source: The CW