Here is the full list of all 9 Impossibox achievements.
You beat the game without dying! WHAT THE WHAT?!
You did it! Sort of. Baby steps you know?
Okay! You made it halfway!
You made it to the final stage! Good luck!
You beat the game! I hope you feel a sense of accomplishment!
Beat the game with 500 deaths or fewer. Sick moves Bruh!
Beat the game with 1000 deaths or fewer. Noice!
Beat the game with 1500 deaths or fewer. Saw, you're pretty good!
Beat the game with 2500 deaths or fewer. I've seen better, but not much.