Kaze and the Wild Masks

As the description says, you need to complete any normal level (non time trial) without collecting any purple crystals. This is actually impossible on the majority of levels, because the purple crystals act like guides and are therefore often directly in your path and completely unavoidable.

The first level this is seemingly possible on is level 2-8, Pumpkin Pyre. This is the level I got the achievement on too. Most of the level is actually pretty easy to avoid crystals. The most important thing is to just make a conscious effort to actually avoid them, since it's easy to forget after always collecting them. When you get to the wind with a platform of crystals, float under the platform. You'll need to go up and over many other crystals throughout the level. Don't worry if you take damage, just avoid the crystals. Play on Casual mode so you can take more hits and have more checkpoints. If you get a crystal by mistake, just die so you start back at the checkpoint before you got it. All that matters is that the level results screen shows zero crystals when it totals everything up.