Here is the full list of all 8 Nebular Crush achievements.
Pass a level without being hit
Pass a level with 90% hit percentage
Get hit 10+ times on a level and don't die
Pass a level without killing any enemies
Kill 100 Spikeballs in arcade mode.
Use full power crush 5+ times on a level
Use small crush 5+ times on a level
Kill 3 enemies with a single dash attack