This episode was actually… not terrible. It wasn't fantastically funny either, but grading on the curve of this season, we'll give it a solid B. While it didn't further any major plotlines, it at least had a lighthearted sensibility about it, and the gang was all hanging out together… and there were Lord of the Rings jokes. So, not total torture.
In the main action, Ted buys a douchey looking wrist-cuff… because some hot 20-year-old was selling them and she's into older men. Turns out that Hanna Marin (as Pretty Little Liar Ashley Benson will always be known to us) thinks Ted is significantly older… like he was in the Vietnam War older. But he goes along with all of this (which includes roller skating in Brooklyn, drinking strange smoothies and partying at a club underneath a Chinatown manhole with "toddlers") because she's insanely hot. And because he's got Barney going through one-night-stand detox and begging for Ted to vicariously bang this girl.
So, though Ted has nothing in common with this girl, aside from her pseudo-interest in Star Wars, he opts to bang her, in what sounds like a variety of ways, and Barney's itch is scratched. And no one even comes out of nowhere with a hoodie and a car and tries to run Hanna over. All's well, until Ted proudly shows off his picture and we find out that it is Barney's never before seen half-sister Carly (from the John Lithgow/Jerry Whitaker side of the family). Barney is grossed out, plans their wedding (much to the delight of some HIMYM fandoms who speculated that Carly might be the mother) and reads from Ted's dream journal (which he's co-opted for his catchphrases and genius one-night stand marketing ideas) about Ted's fear of Whole Foods… until Ted puts a stop to it, and says that Barney's overreaction proves that he is cured of his desire to bang random chicks.
This Barney turn of events bodes well with Robin, who discovers that with her newly-sized engagement ring, New York isn't the sunny Disneyland that she's come to know and love. Instead of getting free coffees and song and dance numbers on her way to work, she gets ignored and can't even get beer. The horror! Marshall helpfully compares this to the One Ring and Harry Potter's invisibility cloak, but he and Lily say that it doesn't really matter if a million people ignore you, so long as you can focus on the one you love… or some similar sappy nonsense. Anyway, eventually Robin realizes that she can just get Barney to get her beer, and the twosome live happily ever after (for today). We even grudgingly tolerated their cutesy "could I love you more" stuff, since at least it made them seem like a real couple… who we want to occasionally punch.
As for Marshmallow and Lilypad, they are having sex, and lots of it (though no sign of Mickey or Marvin in their house). Marshall got one of the leather cuffs, Lily invented a fantasy involving him being a badass and dealing drugs and got super turned on. So Marshall, realizing that sex is a harder commodity to come by post-baby, gamely hides the fact that he's having an allergic reaction to the cuff… well, until he has an enormous left hand. Jason Segel with an oversized baseball mitt-sized hand… well, we had to like this episode a little bit. And then after his trip to the ER, and his admission that he thinks they won't have sex again, he gets horny when she comes out wearing mom jeans and he dreams of Frito pie. To each their own.