"If in the first act you have hung a pistol on the wall, then in the following one it should be fired. Otherwise don't put it there." -
Anton Chekhov This is an idea
stolen shamelessly from Caffinekitty. I wanted to post a list of stuff I consider to be 'on the wall' for How I Met Your Mother. I'm asking for your help - please post additions and comments and I'll incorporate them. This is a NO SPOILERS post entirely based on previous episodes.
People
The Mother: Obviously it's the icon of the show and presumably we'll have to wait for her to appear for real. However, it's likely that her artifacts will reappear (See Yellow Umbrella, but others include playing bass guitar, singing breakfast etc). Interestingly, the Pilot Script puts Ted's daughter's age at 16 when the story begins, meaning she'd be born in 2014. So Ted's could meet the Mom any time in the next three-ish years, but we know it'll definitely be at Barney's wedding that Ted, Marshall and Lily attend and that Ted is the best man (from Season 6).
Victoria: Victoria should be back from Germany by now. Will Ted meet her again?
Heather Mosby: Assuming she got the GNB job, she should still be working in NYC with Barney and Marshall. It makes sense for us to see her again. Barney mentioned "Ted's hot sister Heather" in Home Wreckers, Season 5, but we did not see her.
The Slutty Pumpkin: Will Ted ever meet her again? He's never specifically said he didn't, and he did make such a big deal out of her story.
Milk girl: In Season 1, Ellen the matchmaker does finally set Ted up with a close match. But in the episode Milk, Ted stands her up. Will we ever meet the mystery girl again in any capacity?
Barney's bride: At the end of Season 6, we saw Barney getting married but we don't yet know to who. Robin is the only character that wasn't featured in that flash forward.
Barney's half sister Carly Whittaker: We know she's at university (season 6), but we haven't met her yet. There is speculation that she may be The Mother.
Artifacts
The Yellow Umbrella: The Mother lost her yellow umbrella by accidentally leaving it at the bar in No Tomorrow. Ted went back the next day to look for his phone, found it discarded on the floor and took it as it was raining. Ted later himself lost the yellow umbrella when he accidentally left it at the apartment of his date in Girls vs Suits. Presumably since the Mother was his date's room mate, she now has it back. There have been several red herrings using the yellow umbrella: A woman with a yellow umbrella walks past MacLaren's at the end of Wait For It. Also, when Ted sees Stella at the end of Season 4 (As Fast As She Can), he is carrying a yellow umbrella). However, it's likely (from Season 6, Big Days) that The Mother brings her yellow umbrella to Barney's Wedding, where she meets Ted, as we know it rains at the wedding.
The Scherbatsky Welcome Mat: Someone replaced Robin's custom Scherbatsky doormat after Ted vomited on it (flashback to the Pilot in Game Night). Whether this should be on the wall depends on how you interpret what is meant when Future-Ted does say "Not every secret was told that night, but that is another story. Either the secret was Robin's feelings for Ted, in which case it was Ted who replaced the dormat as an apology and the matter is closed. Or the secret is WHO replaced the doormat, in which case we should find that out eventually. Or even the secret was Robin's Robin Sparkles past, in which caes, again, this is off the wall.
Robin's dogs: Robin sent her five dogs away during her relationship with Ted in Season 2 (in the episode "Stuff"), to live on her aunt's farm in Upstate New York. She sent them away because Ted was uncomfortable with them reminding him of Robin's ex-boyfriends but since this isn't a factor now, wouldn't Robin want dogs again? Of course, in real life Josh Radnor is allergic.
Events
Punchy's Wedding: We know that Ted is the best man. No date for this yet though.
The final slap: Marshall still has one slap remaining from his Slap Bet with Barney. The other four have been used in Slap Bet, Stuff, Slapsgiving, Slapsgiving 2: Revenge of the slap.
Final cigarettes: Marshall quits the day his son is born, and Ted quits two weeks into dating the children's mother. Only Robin and Barney have specific dates for this (2013 and 2017 respectively) We already know that Lily quit smoking the day she decided to try to get pregnant, which was the day she saw Barney's doppleganger in the Season 5/6 hiatus (See Dopplegangers below).
Robin's world travelling: In Something Blue, Future-Ted gives a list of places Robin will live: Argentina, Morocco, Greece, Russia, Japan. So presumably when Robin's career takes off we'll see her live in Morocco, Greece and Russia. Technically she went on Vacation to Argentina, so she could go back there too. Now that Robin works for World Wide News, it's possible that she travels as part of working for that organisation.
The most romantic love story: in 'The Window', future!Ted did say something along the lines of how it was the second most romantic story he'd ever seen. Could that come back into play in the future? People have theorised that the story could be Ted's own, or Marshall and Lily's, but it might not be.
The Three Days of Snow wall: Future-Ted says there are many ill-advised 5-word sentences every man will eventually say in his life: "We should buy a bar" (Ted and Barney, in Three Days of Snow) "I can jump that far" (Marshall pays this off in The Leap) "I'm gonna win her back" (Ted, still on the wall) "I can trust you guys" (Carl, in Three Days of Snow)
Robin's favorite holiday: Future-Ted specifically mentions in the slutty pumpkin episode from season 1 that "Halloween eventually became Robin's favorite holiday". Hopefully we'll get to see how that happens. We know that she didn't attend the GNB party in 2010.
Ted in the green dress: We know that at some time (at least a year after 2010, and when Lily is heavily pregnant), Ted comes into MacLaren's pub wearing a green dress and saying "Okay, now we're even". Presumably like "the goat", this will be explained next season.