Season 5, Episode 1: “Nora”
Who is the strange girl who showed up at Barry and Iris’s original wedding (and made a couple appearances in later episodes of the fourth season)? The team finally finds out in the fifth season premiere, aptly titled “Nora.” (Spoiler alert: she’s Barry and Iris’s daughter from the future.)
Season 5, Episode 5: “All Doll’d Up”
Since Rag Doll apparently appears in a future episode of the sixth season, yet to be aired, it seems pertinent to include his first appearance in this list. Plus, this episode has a really wonderful date between Barry and Iris – and moments to enjoy each other’s company are too few and far between on this series. Eagle-eyed fans should watch for a glimpse of Rag Doll in the window during the Westallen dance.
Season 5, Episode 7: “O Come, All Ye Thankful”
Of all the villains on the show, the Cicadas have to be some of the weakest and least interesting. Still, if you’re curious to know their backstory, this episode fills you in!
Season 5, Episode 12: “Memorabilia”
If you were curious to know if Iris was really a terrible mother in the future, “Memorabilia” makes it clear she really wasn’t. Nora’s attitude notwithstanding. Otherwise, the episode lays the groundwork for Cicada II, and it’s the episode in which Iris finally establishes the newspaper that fans have waited to see since the first season.
Season 5, Episode 21: “The Girl with the Red Lightning”
This entry landed a spot on the list because it seems that the Negative Speed Force will play an important part in the final episodes of the sixth season, and this episode establishes what the Negative Speed Force is, who created it, and why it can be dangerous.
Season 5, Episode 22: “Legacy”
While the fifth season as a whole wasn’t very strong, this season finale wraps up both Cicadas’ storylines and establishes that the date for Crisis on Infinite Earths was moved up due to the events of the season. (Also because Arrow was ending, and they wanted to send it out using the storyline that had been established on The Flash since the beginning of the series.)