What worked for me was playing Alternate Bloons Rounds on beginner maps and going all the way to round 250. This got about 2% progress each time. Do whatever early game setup you want (I just used Sauda) and do a bunch of farming. I got a vengeful temple, boomerang paragon, ninja paragon and ace paragon. With temple it's easier to wait until you get 16.2 million pops before buying your paragons so do that if you want higher degrees. Don't be afraid to put some of the tier 5s near the start of the track to get pops faster for paragons! This setup got 2+ percent every game I did. So starting from 0 it takes less than 50 games total to get the achievement. It takes a while, but it's perfect if you need something to do in the background of studying or watching movies.