It's too bad hard mode only requires that you use positive clues, not negative. I've been trying to push "true hard mode" with my work colleagues. Where every guess must be a potential winner given the information revealed thus far.
So, hard mode, plus no reusing grey letters, plus no using yellow letters in the same incorrect slot.
What, one can re-use a gray letter in hard mode? That's not hard enough!. I find the fun challenge isn't finding the final word but finding valid guesses (i.e. words that exist and aren't using any grays) along the way.
So, hard mode, plus no reusing grey letters, plus no using yellow letters in the same incorrect slot.