Possible Clues:

• Text using whole alphabet
• Sentence using all 26 letters
• Sentence containing all twenty-six letters
• Sentence with all 26 letters
• Greek airline once entertained all the characters here
• Crossword whose answers contain all 26 letters, e.g.
• Alphabetically complete passage
• "The quick brown fox ..." for example
• In the end, this grid is something painful to beat
• This puzzle's theme is one