WARNING: The following article contains spoilers for the latest episode of Gotham, "Trespassers," which aired Thursday on Fox.

Gotham's Season 5 mega-trailer revealed that new villains from Batman's rogues gallery would join the series alongside the already quite large cast of foes currently featured on the show. Characters such as Bane, Mother and the Mutants, among others, would be joining returning villains such as Penguin, Scarecrow, Riddler, Mr. Freeze and the Joker Jeremiah Valeska. And yet, through all of its marketing, there is still one return that Gotham managed to keep secret.

In "Trespassers," the second episode of Gotham's fifth and final season, Peyton List made a surprise return as Poison Ivy. And in a bit of more bad news for Gotham City, Ivy's got some comic book-inspired plans of her own.

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In the episode, Ivy resurfaces after Bruce Wayne goes looking for someone named the Witch, a mystical woman whom he believes has the power to help Selina Kyle walk again. What he doesn't expect, however, is to discover that this Witch is actually someone he knows. He finds Ivy in a park where she has taken refuge, and where she has been killing men to feed to the growing plant life.

She explains that once Gotham's bridges were destroyed and the city cut off from the rest of the mainland, the park began to change, reaching out to her. Now, there are plants growing underneath it that she never knew existed, and she's feeding them her victims so that they may flourish once more.

In the comic books, Poison Ivy is often seen backed up by gigantic, man-eating plants that she has, on occasion, unleashed on Gotham (and, once, the whole world). If these are the same plants currently growing underneath Ivy's park, then the villain may be an even bigger threat than we believed. Is this a simple nod to the source material, or hints at a future storyline in the "No Man's Land" saga?

Gotham Ivy Pepper

When Gotham first premiered, a much younger Ivy Pepper was played by Clare Foley. Then, after going through a rebirth, Maggie Geha replaced Foley as an older Ivy in Seasons 3 and 4. Finally, Peyton List joined the cast after Ivy went through yet another transformation in Season 4. As is stands, it's unclear if List's return as Ivy in Season 5 is a one-off, or if she will return later in the season hellbent on manufacturing some topiary nightmares with which to further threaten the city's citizens.

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Airing Thursdays at 8 p.m. ET/PT on Fox, Gotham stars Ben McKenzie as James Gordon, Donal Logue as Harvey Bullock, David Mazouz as Bruce Wayne, Robin Lord Taylor as Penguin, Camren Bicondova as Selina Kyle, Erin Richards as Barbara Kean and Sean Pertwee as Alfred Pennyworth. The fifth and final season premiered on Jan. 3, and will run for 12 episodes.