As a detective solving the mystery of the crossword clue ‘Old-fashioned “Whoopee!”‘, my first insight was to think about words that have a similar meaning to “Whoopee“. I started by looking through the letters that were available in the grid and identified some of the letters that could fit into the answer. The word “HUZZAH” quickly came to mind, and upon further investigation, I learned that “HUZZAH” is a word that was often used in old-fashioned times to express excitement or joy.
Given the context of the clue, the fact that “Whoopee” is an outdated expression, it makes sense that the answer is a word that has also fallen out of common usage. Additionally, the exclamation point at the end of the clue signals that the answer should be a celebratory word. “HUZZAH” perfectly matches both of these criteria, and I am confident that this is the correct answer to the mystery.