I had no idea that this was even an achievement but apparently there is a garden gnome that appears at the beginning of Half-Life 2: Episode 2 that you can potentially carry throughout the game and put into the rocket at the end. To do this requires the patience of Job and a maddening predilection towards completism.
Tom Francis completed the game in gnome mode and his comments and screenshots are hilarious.
Halfway through reviewing Half-Life 2: Episode Two for PC Gamer about a month ago, Valve PR Doug Lombardi asks me if I know about the gnome achievement.
“Did you find the gnome near the start?”
“You have to put him in the rocket before it launches.”
“But isn’t that right near the end of the game?”
“Doesn’t that mean you have to-”
“Oh I’m so doing that.”
A month or so later, I have.
Others have created little gnome tableau placing the fellow in the frame as a stand-in for Freeman. While I didn’t like the ending to Episode 2, this definitely makes the game 100% better for me.