This achievement requires paid content.
To earn this achievement, you must unlock 39 medals cumulatively in Game Room. Each medal is only counted once. If you unlock the Bronze Time Spender, and then unlock the Silver Time Spender, that is still only one medal.
Medals can only be earned in ranked play, and in games that you either own, are purchasing sessions with using the 40 MS point option, or on games that your console is licensed to (i.e. Someone else bought that game on your console). Medals can NOT be earned in demo play, classic play, or if you are using tokens to play a friend's machine.
There are three medal varieties:
Point Buster : These medals are awarded when you reach certain score targets.
Survivalist : These medals are awarded for surviving a set amount of time in a single play.
Time Spender : These medals are awarded for cumulative game play.
Every game has a Time Spender medal. Note that Time Spender medals can be earned in ranked or classic play, and are cumulative between game sessions. Most games also have a Point Buster and Survivalist medal. Medals "upgrade" as you progress. What this means is that if you have a Bronze medal and suddenly earn a Silver medal, you only have a Silver Medal. This will only count as 1 medal. Bronze, silver, and gold medals all count.
A chart of which games have which medals available, and the goals that must be met to get those medals is posted here:
http://www.tinyurl.com/GameRoomMedalChart