The star of the popular CBS comedy appeared on "Jimmy Kimmel Live" on Tuesday ahead of her show's series finale next Monday to discuss her upcoming project -- wait for it -- her 5-year-old daughter Satyana's birthday party this weekend.
"When did it change? Because when I was a kid, when I went to birthday parties I didn't get a present," the actress vented. "But now suddenly it's not good enough to just throw them an awesome party. You have to then give kids that come to your house, you have to get them presents too. They walk away with like swag!
"And then I get a little crazy because I go on Pinterest and I'm like 'Oh, I can make all that!'" she continued. (Pinterest, you son of a ... ! At least that's what Lily Aldrin would say...)
So now, the "Buffy the Vampire Slayer" alum, who celebrated her 40th birthday this week with "a quick breakfast," is hand-crafting mermaid-themed "crap" that includes fabric mermaid dolls, treasure chests and wands for 16 children.
Hannigan is married to actor Alexis Denisof, who appeared on "Buffy" and guest starred on "HIMYM" as sleazy anchor Sandy Rivers. The couple has two daughters, Satyana and Keeva. She's also got Denisof helping her stain treasure chests and giving input on birthday cakes.
"'That's a great one to end on!' -my husband to me after I showed him yet another amazing cake on Pinterest," she recently tweeted.
As for her professional life, the full-time mom has signed on to a CBS pilot called "More Time With Family," which she's already lobbied her Twitter followers to watch.
Though the majority of the actress' "Kimmel" appearance was eclipsed by the obsesessive arrangements for her eldest's birthday, she did get a chance to talk about the series' much-hyped finale in which Ted, played by Josh Radnor, will presumably meet the titular mother of his children.
After nine seasons, the show starring Radnor, Hannigan, Jason Segel, Cobie Smulders and Neil Patrick Harris is already in syndication on various networks and has prompted a Greta Gerwig-led spin-off called "How I Met Your Dad." And though the finale hasn't aired yet, its emotional content had many of the cast members in tears.
"It was [sad]. I killed a lot of trees with my crying," she told Kimmel, alluding to the glut of tissues she consumed with her waterworks.
"The last table read -- you know we all do love each other so much -- I would say 99% of the room was crying -- that's executives and everything -- we were laughing and crying; it's not a sad show."
She added that she did her "grieving" while doing the last episode, because she knew that she wouldn't see the cast and crew all together in the same place again.
When Kimmel jocularly pressed her about the show's "surprise ending," one that could mean a sinister fate for either Ted or the mother, Hannigan was mum and pretended he was again talking about her daughter's birthday party.
"I think that the writers really wrapped the show up the way the fans would want it to be wrapped up and they're going to answer all the million questions that everybody has and more," she said.
As for her own feelings about the show coming to a close, she reiterated her grief levels to Time magazine.
"You know, I think I did most of my grieving at the end of the season because now I feel like, 'Oh, that was great!' This ninth season was shot around so many different schedules, and it was such a weird season that it was almost like our methadone," she said. "It was a nice way of getting used to not seeing everyone every day of the week. So it prepared us for the finality of it all."
And at a PaleyFest panel last week, she said that the ending really sunk in when she was shooting a scene with her on-screen husband, played by Segel.
"[I thought], 'Wow, this is the last time I'm going to be lying in bed with this bozo,'" she said (via Variety). "Everything was so sentimental that week. I think this whole season we just got to really appreciate how fantastic this whole journey has been. We didn't take it for granted the way we did [before]."
Follow Ministry of Gossip @LATcelebs.