Warning: contains spoilers for Flashpoint Beyond #0!
As the fractured timeline of DC's Flashpoint event returns, a new mystery begins that seems to suggest the Reverse-Flash is getting revenge for his death during the blockbuster story. This can be seen in Flashpoint Beyond #0. The issue is written by Geoff Johns and drawn by Eduardo Risso.
The Thomas Wayne of the Flashpoint timeline has had quite a journey thus far. In a world where Bruce Wayne was murdered in crime alley, Thomas descended into the role of Batman. Then his wife Martha went insane and became that timeline's version of the Joker. Thomas fought alongside Barry Allen to restore the true timeline, even running Reverse-Flash through with a sword in the event's final battle. After Barry Allen 'fixed' time, Thomas' world should no longer exist, but after a series of adventures through the multiverse as a member of Justice League Incarnate, he's now appeared back on his supposedly erased world after being killed by Darkseid.
In Flashpoint Beyond #0, Thomas remembers everything, and tries to fix things again. After Thomas fails to recreate the Flash with his own world's Barry Allen, a telltale yellow flash speeds past, taunting him. It looks like this is the Reverse-Flash, back to mock the man who killed him in their last conflict. It's not yet clear if the Reverse-Flash was responsible for the return of the Flashpoint timeline or was just resurrected along with it, but with his incredible abilities, he's more than capable of taking revenge for Thomas killing him. Just being back in his home reality is causing Thomas Wayne to lose control, and Reverse-Flash's taunting helps cause Batman's frustration and confusion to boil up into incredible violence.
In the original Flashpoint event, Reverse-Flash was the initial suspect for the changes to time, with Barry Allen believing Eobard Thawne had gone back to change events. Ultimately, it was revealed that Reverse-Flash was innocent, and it was Barry himself who'd broken time in an attempt to save his mother. However, Thawne has always defined himself in comparison to Barry, so it would make sense that this time, he really did find a way to bring this world back. Flashpoint Beyond is a major story that will go on to affect the DC multiverse, so it's also possible Reverse-Flash has far grander plans than just tormenting Thomas Wayne, seemingly leaving the lethal Batman a cryptic message that states, "Everything matters."
An egotistical maniac, the Reverse-Flash is known for holding a grudge. Typically, the Flash is his arch-enemy, but since Thomas Wayne killed him, it fits perfectly with Reverse-Flash’s personality to make Thomas' life hell. Plus, as a time-traveling speedster, Reverse-Flash is more than capable of resurrecting the world that Thomas worked so hard to erase. With super-speed making him invisible to the naked eye, the Reverse-Flash can be in the background in nearly every scene of the story without the characters of Flashpoint knowing, making him the perfect new nemesis for Thomas Wayne's unstable Batman.