This episode aired on May 23, 2017, which was the date on which Savitar originally killed Iris.
Savitar mentions DeVoe as he recalls his memory in S.T.A.R. Labs. This is a reference to Clifford DeVoe, a villain known as the Thinker. This is the second time a reference on DeVoe was made. The first being in Abra Kadabra, by Abra Kadabra. Savitar stated that it "hadn't happened yet", foreshadowing an appearance from The Thinker in Season 4 in which he will become the main villain throughout that season.
Savitar mentioning DeVoe is quite similar to when Ra's al Ghul mentions Damien Darhk in the season 3 finale of Arrow in which both Ra's al Ghul and Savitar are the main villains for the third seasons of both the Flash and Arrow in which they both mention the villians to both of the main protagonists in the season finale of season 3 in The Flash and Arrow in which those villains become the main antagonists in the next season such as Damien Darhk has become the main antagonist for season 4 of Arrow while DeVoe will become the main antagonist for season 4 of The Flash.
Cisco refers to Savitar as "Two-Face" after he was rescued by Gypsy. This is a tongue-in-cheek reference to the comics villain Harvey Dent, aka Two-Face, an antagonist of Batman who also has the left half his face severely scarred.
The story that Barry talked to Savitar about could be a reference to the beginning of the animated DC movie "Justice League: Flashpoint Paradox". This storyline was also the catalyst for Season 3.
The scene where Savitar holds Cisco while vibrating his hand and telling him that he will die "the same way twice" refers to his death in the erased timeline in Out of Time.
Savitar is killed the same way that The Rival was killed in Flashpoint. The Rival was shot in the back by Joe as he was trying to attack Barry from behind, and Savitar was shot by Iris when he was trying to do the same to Barry.
The Speed Force lightning storm above Central City is a reference to a similar storm that appeared in the first issue of the 2016 Flash relaunch comic that infused several citizens with the Speed Force. It's currently unknown if the one seen in the episode has had any similar effects.
In the final scene, Iris calls Barry "Wally".
In the previous episode, H.R.'s last word to Cisco is "Till next time" and salutes him after he puts on his hat.
However, in this episode the flashback shows it was changed to "Till the next one" and H.R. slightly tips his hat.