Here is the full list of all 12 Nephenthesys achievements.
Collect 125 upgrades.
Kill 2500 enemies.
Beat stage 5.
Score more than 50,000 points in a single run.
Collect 50 upgrades.
Beat stage 4.
Kill 1000 enemies.
Beat stage 3.
Beat stage 2.
Beat stage 1.
Kill 100 enemies.
Collect 5 upgrades.