Here is the full list of all 8 Alien Shepherd achievements.
You've reached the end of the game, congratulations !
You managed to finish the game without dying.
You found a secret, keep looking !
You found all secrets in the game, I think we can say that you're done now.
You make one with the Jellyfish.
You've reached the end of the game without checkpoints, congratulations !
That's some dedication !
You reached the end in less than 20min !