The gang doesn't believe that it's safe for Ted, a single man, to hang out with Zoey, a married women. Meanwhile, Marshall and Robin decide to spend some time together. At the same time, Barney and Lily have some strife going on. If only Future!Ted can remember what...
This episode provides examples of:
- A Rare Sentence: "Once a mermaid gets pregnant, she becomes a manatee again. ...never thought I'd say that sentence..."
- Breaking the Fourth Wall: Lily and Barney get noticeably bored and impatient as Future!Ted struggles to remember why they were fighting.
- Captain Obvious: "Wait! Barney isn't a woman!"
- Chekhov's Gun: The titular mermaid theory winds up being the key to Future!Ted remembering what went down in Barney and Lily's subplot.
- The sound of ticking that accompanies the "Mermaid Theory"note ...
- Continuity Snarl: Marshall and Robin find it awkward to hang out alone, despite the fact that they spent a couple of season-four episodes alone at Minnesota- and Canada-themed bars.
- Eureka Moment: After Marshal explains the "Mermaid Theory"'s exceptionnote , Future!Ted remembers why Barney and Lily were fighting.
- The Friends Who Never Hang: Marshall and Robin realize they never spend any time together independent of the group. When they go out alone together it's... awkward.
- Here We Go Again!: Defied: after Barney and Lily's subplot, which suffered from Future!Ted's mad memory causing bizzare stuff to happen, it finally sorted out at the end, we see Ted walk in, wearing a green dress, telling Barney that they were even now. What seems like another case of Future!Ted's bad memory, he immediately clarifies that there is an explanation.
- I Have to Wash My Hair: Ted invites the gang to a boring event, and they exaggerate this trope to emphasize their lack of interest.Lily: Sorry, I'm, uh, I-I don't know, washing my hair.
Marshall: Running the water.
Robin: Holding the towel.
Barney: (beat) And I'll be at home trying to get over the fact that no one invited me to the big hair-washing party.
- Mind Screw: As a result of Future!Ted not remembering things clearly, a motorcycle spontaneously drives through the bar, Barney calls himself a woman, and Barney manages to make a beer bottle float in front of Lilynote .
- Out of Order: Barney and Lily's subplot, as it happens, actually takes place some time during the events of "Now We're Even".Future!Ted: Wait! That's it! That's what Barney and Lily were fighting about! The "Mermaid Theory"! But their argument didn't happen at the same time as all this other stuff. I'm literally in the wrong year!
- Rage Breaking Point: After Barney supposedly make a beer bottle float in mid-air, Future!Ted gave up trying to remember that story.
- Tempting Fate: After he realizes he got Barney and Lily mixed up in telling their story, Future!Ted declares that the story will now make sense. Cue the floating beer bottle.
- Twitchy Eye: Marshall when the stress of not being able to hold a conversation with Robin gets to him. Robin catches on, and she catches the twitch as well.
- Unreliable Narrator: Played for Laughs with Future!Ted struggling to remember the details of Lily and Barney's fight.Future!Ted: Kids, here's one thing I do remember: I was pretty sure I was going to die that night.
- Wham Sound: After Ted and Zoey confirm that they don't have feelings for each other, the sound of ticking starts up.