Thanks to Marcos Aspira, runs now count when you die, "
Mine unlocked when I was trying the Baphomet stage over and over."
As of the original game release, a run is considered completed by beating the boss at the end of the stage. This will add to your run count as well as meters run in total, which is a challenge and you will need to accumulate 20,000 meters to complete it entirely.
The quickest way to grind this is to play the first stage over and over again with the gunslinger fox. The fox is the quickest character and the first stage is the shortest at only 120m per run.
If you are looking to complete the game and unlock all characters, 600,000 coins total, this achievement will unlock naturally.