When the bill came, we all had to 'pony up'. [='pay up'] = We all had to 'pony up' for the bill.
As a knitter, I'm a 'one-trick pony': I can only knit scarves.
a musician who was a 'one-trick pony' and then faded away
(..) I'll send them to Santa's workshop at the North Pole. Oh, please. There's only one fat guy that brings us presents, and his name ain't Santa. Uh-- A pony? Oh, Lisa, you've asked for that for the last three years, and I keep telling you Santa can't fit a pony into his sleigh. Can't you take a hint? But I really want a pony, - and I've been really good this year. - Oh, dear. Maybe Bart is a little more realistic. - A tattoo? (..)1989 TvShow: The Simpsons Title: Simpsons Roasting on an Open Fire Season: 1 Episode 1