Most unpleasantly old and mildewy Crossword Clue

 The answer to the crossword clue "Most unpleasantly old and mildewy" is MUSTIEST.

Musty is an adjective that means "having a stale, unpleasant smell, especially from being kept in a closed place or from being damp." It is often used to describe old books, clothes, or furniture that have been stored away for a long time.

The superlative of musty is mustiest, which means the most unpleasant or stale smell.

Here are some examples of how the word "mustiest" might be used in a sentence:

The mustiest smell filled the air as I opened the door to the attic.

The old clothes in the back of the closet were mustiest of all.

The abandoned house had a mustiest smell that made me want to sneeze.

I hope this helps!