- "Oh, why should the spirit of mortal be proud? Like a fast-flittering meteor, a fast-flying cloud, a flash of the lightning, a break of the wave, he passes from life to his rest in the grave."
- —Joan Williams quoting William Knox
Faced with the news of his impending death, Barry’s resiliency suffers as he struggles to fight fate. Meanwhile, Cecile’s career as a D.A. conflicts with her identity when she crosses paths with a villainous meta-human.
- The episode's title is a reference to a line from the William Knox poem "Mortality", which Joan Williams reads to bring Barry back to consciousness.
- The episode shares its title with Crisis on Infinite Earths eponymous eighth issue, which featured Barry sacrificing himself to save the multiverse. Knox's poem is also seen on the last page of the issue.
- Jay tells Barry that he had spent a year tracking the spread of antimatter throughout the multiverse, showcasing a map of the Earths he had discovered thus far. The map featured annotations from Jay, which ranged from the Earths that have the best vegan food and tequila, to which superheroes call which Earth home. Towards the top of the list, next to Earth-51 (his home Earth in the comics), is the name "Thaddeus Brown." Both Thaddeus and Earth-51 were previously mentioned in "". In the comics, Thaddeus was the first to hold the mantle of Mister Miracle.
- Also on his map, Jay predicts that the antimatter wave would next appear on Earth-2. This was seen in the episode "", which aired directly after this one.
- This is the first episode to feature Killer Frost but not Caitlin in any capacity, leaving Barry and Iris as the only characters to appear in every episode.
- In the recovery bed, Barry tells Joan that she should have used Lady Gaga to reawaken him. This is a reference to "", where Caitlin and Cisco played a Lady Gaga song when Barry woke up from his coma.
- It was also used again before in "" when the team needed to awaken Barry after he was brought into S.T.A.R Labs after his time in the Speed Force.
- The man who saved Esperanza was wearing the logo of the Black Hole organization, which in the comics was connected to Godspeed.
- Barry's vision shows Cisco suited up in his Vibe suit again, suggesting that he'll somehow regain his powers.
- However, since Barry viewed billions of potential futures, it is possible that what Barry saw was one alternate timeline/future where Cisco never gave up his powers.
- Cisco calls Killer Frost a White Walker, referencing Game of Thrones.
- Barry wears the same clothing he wore in "" when he time traveled.
- Cisco asks Killer Frost, "what did you do with your Tuesday?" a breaking the fourth wall joke as the show airs on Tuesday.
- Gideon suggests Barry's top speed is 1/80 that of the speed of light, or about 2325 miles per second.
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