The CW Network's The Flash airs its final episode of 2015 tonight with the fall finale entitled Running to Stand Still, airing at 8 PM ET. To get fans ready for this new episode, The CW Network has released a new producer's preview, where executive producer Gabrielle G. Stanton teases that a trio of villains will be causing havoc for Barry Allen, The Trickster (Mark Hamill), Captain Cold (Wentworth Miller) and The Weather Wizard (Liam McIntyre). The producer also teases that Barry learns Shantel VanSanten's Patty Spivot may not be the best person to work with on this case, since The Weather Wizard killed her father.

The Flash episode Running to Stand Still centers on Mark Mardon AKA The Weather Wizard (guest star Liam McIntyre), who returns to break Leonard Snart AKA Captain Cold (guest star Wentworth Miller) and James Jesse AKA The Trickster (guest star Mark Hamill) out of Iron Heights. Barry must stop these rogues from taking over Central City during Christmas. Meanwhile, Joe and Iris meet Wally West (Keiynan Lonsdale). This episode will mark Wally West's debut, before he returns in the back half of this season.

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In addition to this preview, we also have a heart-wrenching clip that sets up the introduction of Wally West, where Iris (Candice Patton) tells her father Joe (Jesse L. Martin) that his ex-wife Francine (Vanessa Williams) was pregnant when she left him, and that he has a son named Wally. It isn't known how both Iris and Barry (Grant Gustin) found out about Wally, but all will be revealed tonight. If that wasn't enough, we also have two more clips. The first features Barry learning that Weather Wizard and Trickster have given 100 children presents with bombs inside. The only way to stop it is for Barry to let the Weather Wizard "end him," publicly. The second clip features the mysterious Zoom attacks Harrison Wells (Tom Cavanagh).

Keiynan Lonsdale was cast as Wally West back in August, but it was never revealed when this character would debut on The Flash. In the comics, Wally is the nephew of Iris West, played by Candice Patton in the series. He eventually turns into the character known as Kid Flash, after an accident that is reminiscent of how Barry Allen (Grant Gustin) gets his powers. We still don't know if Wally will turn into Kid Flash at any point during this season, but it's certainly possible.

The CW hasn't announced when The Flash will return from its mid-season hiatus quite yet, but we do know that both The Flash and Arrow will be joined by another superhero series, DC's Legends of Tomorrow. The network announced last month that DC's Legends of Tomorrow will air on Thursday, January 21 at 8 PM ET, giving fans three nights of superhero shows in a row. Take a look at these new videos from the last Flash episode of the year.