While the team deals with a new villain using Krei's portal tech to commit robberies, Megan confronts Hiro about being a vigilante and threatens to tell Chief Cruz the truth.
Tropes in this episode include:
- Blatant Lies: When Hiro shows Megan their Base, when the rest of the team sees her they try to act like they are making candy, even after the dramatic reveal of their suits.
- Call-Back: Sirque steals the data for Project Silent Sparrow, the portal technology from the movie. Like in the movie, it destabilizes after repeated use.
- Comical Nap Drool: Referenced by Krei during a phone call with his mother near the beginning of the episode.Krei: Last time, Harold Stubing fell asleep, right on Margorie Templeton's shoulder! A single strand of drool fell like an angel's tear!"
- Continuity Nod:
- The Krei Tech phones are still slippery.
- Apparently, the Buddy Guards are still prone to malfunctioning, if Chief Cruz's complaint to Krei is anything to go by.
- Baymax's original body is still floating around in the portal dimension.
- Ear Ache: After Hiro brings Megan to the base, GoGo pulls Hiro by his ear to the other side of the room to explain himself to the rest of the team.
- Even Evil Has Standards: Sirque may be a criminal, but she helps Hiro stabilize the portal when the flaw in the technology is explained to her and promises to iron it out before using it again.
- Fighting Across Time and Space: In the climax, Hiro chases Sirque as she uses her portals to go all over the city, including Fred's mansion while Heathcliff is cleaning.
- Hypocritical Humor: Fred tells Hiro that telling people your secret identity is among the worst things a superhero could do, along with going back in time to fix your mistakes. Almost immediately afterwards, he suggests that Hiro should do just that. Wasabi tries to explain what Fred just did, but then reconsiders and shrugs it off.
- Innocently Insensitive: Megan, already uneasy knowing that Hiro is part of Big Hero 6, tries to speak to him about it but Hiro is too preoccupied with the info leak at Krei Tech. While Megan would normally dismiss his seemingly-flighty tendencies as Hiro "acting weird," knowing he's deliberately keeping secrets from her only upsets her more.
- Mythology Gag: Hiro's new suit of having jets on all of his limbs seem to be based on Rocket Cat from the original comic.
- Oblivious Janitor Cut: Hiro chases Sirque into the Fredrickson mansion, as Heathcliff is cleaning. He is listening to music on his earbuds, so he is not aware of the mess Hiro and Sirque are making until they are gone. He turns around to see the damage and sighs.
- Police Are Useless: Megan claims that the police are enough to protect San Fransokyo, but Hiro rebukes her in saying that the police just don't have the ability to handle villains, unlike Big Hero 6.
- Hiro's argument is validated when the police try to apprehend Sirque at the museum. They sic the Buddy Guards on her, only for her portal to send them to the bay. The police retreat in fear of her portal tech.
- Portmanteau: Like all other locations mentioned in the series, Sirque worked as an acrobat in Lyontreal, combining the French city of Lyon (famous for the Roman Amphithéâtre des Trois Gaules) and Montreal (home of Cirque du Soleil).
- Pun-Based Title: It is a play on "mortal enemy".
- Secret-Keeper: By the end of the episode, Megan makes the tough decision to keep Big Hero 6's identities secret.
- Speak of the Devil: The Team is discussing what can they do to stop Megan from finding out their identities, just as Hiro leads her into their base.
- Shout-Out: When Hiro is testing his new suit, it is very similar to how Tony Stark tested out his first Iron Man Suit.
- Villainous Rescue: Sirque stops Hiro from falling into the unstable portal, then holds him in place so he can stabilize the portal.
- What the Hell, Hero?: Megan is not happy with Hiro over keeping secrets from her all this time. She eventually comes around and forgives him once she witnesses him put his life on the line for the city's safety.
- The team also directs this towards Hiro for bringing Megan to the base without their permission.
