Point Leader Achievement
Achieve 999999 points in a single playthroughYou can easily complete this in Boss Rush mode, which is unlocked after completing the game. You will face the three bosses from the game, without any enemies in between. Defeating each awards 100,000 points. So in order to reach the required score, you need to defeat the first two bosses and then die to the final boss and select Retry. You will spawn at the beginning of the Boss Rush, but keep all your previous points. So just rinse and repeat until the achievement pops.
See the video below for more information.