Database: superhero
Question: Among all superheroes in Marvel Comics, identify the percentage of 'good' superheroes.
SQL: SELECT CAST(COUNT(CASE WHEN T3.alignment = 'Good' THEN T1.id ELSE NULL END) AS REAL) * 100 / COUNT(T1.id) FROM superhero AS T1 INNER JOIN publisher AS T2 ON T1.publisher_id = T2.id INNER JOIN alignment AS T3 ON T1.alignment_id = T3.id WHERE T2.publisher_name = 'Marvel Comics'