Achieved by watching a player uploaded video of a replay that was uploaded to the leaderboards.
NOTE: May immediately pop when accessing leaderboards, without needing to start or watch a replay (Credit to Dwaggienite)
You can access these replays by viewing the caravan mode leaderboard, and hit "download replay".
There should be a few up there, as top players tend to upload their replays. If you have trouble, I should still have a few basic replays uploaded. It may also work if you view your own uploaded replay via the leaderboard.