How many characters are there in Twelfth Night?
Twelfth Night refers to Title = 'Twelfth Night'
SELECT COUNT(DISTINCT T4.id) FROM works AS T1 INNER JOIN chapters AS T2 ON T1.id = T2.work_id INNER JOIN paragraphs AS T3 ON T2.id = T3.chapter_id INNER JOIN characters AS T4 ON T3.character_id = T4.id WHERE T1.Title = 'Twelfth Night'