The requirement for this achievement is building your combo to 100. At 50, the colors go crazy. When you reach 100, everything turns white. The key to getting the combo up to 100 is the Scythe.
To get the Scythe, you need to spend all your glyphs re-rolling shop inventory. The Scythe will then be available for 1 glyph. Now carefully 5-combo the mushrooms on the ceiling to get a glyph so that you can buy it.
I used the Brick Head (so I wouldn't break apart if I took damage), the Scythe, and the Shark Fin, which causes an insane burst of scythe madness when used. I combo'd through the first four areas in Cave World (killing most enemies along the way), then kept my combo through the shop with the mushrooms on the ceiling, then used a Shark Fin barrage in the boss room and got my combo to 100, unlocking the achievement.