We already knew The Mother was at a St. Patrick’s Day party that Ted and Barney went to in 2008.
In the 200th episode, we learn her side of things:
But The Mother left the party early, only to meet none other than The Naked Man.
Which is why Ted accidentally takes her umbrella!
On Ted's first day teaching (the wrong class) at Columbia, we knew she was in the auditorium.
And now we know that's how The Mother meets Ted's ex-girlfriend Cindy. They sit next to each other!
And she's there when Ted's running to the right class.
That chance classroom seating is how The Mother ends up living in the same apartment as Cindy!
Where we learn that Ted and The Mother are basically the same (dorky) person.
And, perhaps most importantly of all, we discover that she had heard of Barney and Ted's fake bar called Puzzles!
And that she gets the name!
We also discover how she gets the yellow umbrella back!
Cindy, annoyed that Ted is only interested in her roommate's stuff, makes him leave. He sees The Mother's ankle on his way out the door and ends up accidentally returning her yellow umbrella when he leaves it behind.