It was unclear what to do with the mystery word, so I skipped it. It wasn't until the first round that I realized the mystery word wasn't supposed to be found on the board, but it's just a random word. Also, the text input is hidden behind the "found words" box, so I have no idea what's happening with my input and why it didn't count my answer.
Maybe I’m tired, but I found the first level to be really challenging. I think starting a bit easier to give the player some early success will do better to hook them in and help them understand the game mechanics beyond just what the tutorial offers. I was struggling, and ultimately gave up when I was one letter away from unlocking the mystery word.