The Mystery Shack {Riddle Solved}

[Via]

Bump for hints. They're in the first post and here:

 

Hints

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• If you're having trouble solving the key, think about the letters I used
  • A rather big hint is that there's one letter "missing", since I didn't use any of the letters associated with that one
• Some people might see the key more easily than others, depends on their interests
  • Again, though, I still consider this a fair riddle because you should've learned about this at least once before
  • Tbh you don't even really need this prior knowledge if you can pick up on the letters I used
• The encrypted question is an actual question, there's not a hidden message like it was in the last riddle
• Probs obvious but each line is one word, that seemed to be the easiest way to write it out for you to see clearly
• Might give additional hints tomorrow too, remember you can also ask questions in the thread!