This achievement is for scoring 15000+ on the game TOTC, which you unlock for finding all 9 pieces of the disc. Scoring 15000 is not too difficult, but will take a few tries. I recommend not using the power up for getting 5 of the collectibles, as by not using it, more enemies spawn, and further collectibles give 500 points. More enemies spawning allows for faster point gaining, and some good dashes across the screen can clean up the masses pretty nicely. I recommend dashing back and forth to clear the ground mobs as often as possible, and uppercutting when the ground is fairly clean to clear up some air space. You can also dash in mid air to clear out lots of flying enemies, but be aware that some of them have armor and will knock you out of the sky upon contact, normally resulting in taking damage below. I also highly recommend taking out the big enemies on the ground asap, as they stop you from cleaning up. You can do this by smashing from above, or if you're careful, an uppercut while near them will also take them out.