Even after using the diamond for it's only actual function, the player can take more coal and use it to make more diamonds.
When you click the toolbox after taking the ladder, the text says there's "noting" useful in there.
When you leave the conversation you can have with Karl by using him on yourself, you say he doesn't "breath". "Breath" is a noun; the verb is "breathe".
Also, needing to get the flowers specifically from your ship for a puzzle feels a little arbitrary given that there's plenty of flowers in the environment itself which you could logically use for the same puzzle.