- "I have spent so much time with you guys. You're my family now. You deserve to be happy and if I can be a small part of making that happen, then this will be worth it."
- —Zari Tomaz to the Legends
After the team returns from a mission, Zari finds herself trapped in a time loop that results in the Waverider blowing up over and over again. Zari soon begins to suspect that the answer to stop what is happening might lie hidden among her fellow shipmates’ secrets. But in investigating them she starts to understand her place on the team.
- Brandon Routh as Ray Palmer/The Atom
- Caity Lotz as Sara Lance
- Maisie Richardson-Sellers as Amaya Jiwe
- Tala Ashe as older Zari Tomaz
- Amy Louise Pemberton as Gideon
- Nick Zano as Nate Heywood
- Dominic Purcell as Mick Rory
Special Appearance By
Special Guest Star
- This episode's title is a reference to the eponymous line "Mamma mia, here I go again" from the ABBA song "Mamma Mia", which is spoken by Zari Tomaz before the second Waverider explosion during the time loop.
- This is the first episode to feature Keiynan Lonsdale (Wally West) as a series regular. However, he is billed as a special appearance in the ending credits, presumably to maintain an air of suspense.
- Nate has Zari reference the 1993 film Groundhog Day in order to explain her time loop predicament to him.
- The scene where Zari stuffs a donut into her mouth could be a reference to a similar scene in Groundhog Day where Bill Murray's character stuffs cake into his mouth.
- Ray likens Zari's situation to the Star Trek: The Next Generation episode "Cause and Effect", in which the characters experience a similar time loop leading to the repeated destruction of the USS Enterprise.
- Zari is shown playing the song Vivaldi's Concerto No. 4 in F minor, Op. 8, RV 297, "Winter": Largo, referencing actress Tala Ashe's real-life experience in playing the violin.
- Amy Pemberton makes an appearance as Gideon in human form. This is the second time she has appeared in person after the second-season episode "", although she made a pseudo-appearance in a photograph in the third season premiere "".
- The beer Mick drinks has a Batman logo.
- Hawkgirl's helmet is seen in Zari's "fun montage" scene, though Zari adopts a Catwoman-esque pose while wearing it.
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