Final answer:
The word that fits the clue 'A disguise that delights or frightens' and the pattern C_S__M_ for the Halloween-themed crossword puzzle is 'costume'.
Step-by-step explanation:
Based on the clue provided and the letter pattern “C_S__M_”, it seems that the word you are looking for to complete your Halloween-themed crossword puzzle is “costume”. A costume can be either a disguise that delights, as with a funny or clever outfit, or frightens, as with a scary or ghoulish get-up, especially popular during Halloween celebrations when people dress up to go trick-or-treating or attend parties.