Hola.
Te hace falta indicar el valor del parámetro now_date.
Tienes varias formas.
query = "INSERT INTO games (name, description, url, category_id, category_parent, width, height, image, published, filetype, instructions, date_added, advert_id, highscores, mochi_id, seo_url, submitter)\
VALUES ('Tesla', 'this is just a description', 'http://juego..swf', 2, 0, 480, 248, 'http://localhsot.jpg', 0, 'swf', 'This are the instructions', '%(date)s', 1, 1, '', 'some-game', 0)" % {'date': now_date}
cursor.execute(query)
Otra forma
query = "INSERT INTO games (name, description, url, category_id, category_parent, width, height, image, published, filetype, instructions, date_added, advert_id, highscores, mochi_id, seo_url, submitter)\
VALUES ('Tesla', 'this is just a description', 'http://juego..swf', 2, 0, 480, 248, 'http://localhsot.jpg', 0, 'swf', 'This are the instructions', '"+ now_date.strftime('%Y-%m-%d') +"', 1, 1, '', 'some-game', 0)"
cursor.execute(query)
Otra más
query = "INSERT INTO games (name, description, url, category_id, category_parent, width, height, image, published, filetype, instructions, date_added, advert_id, highscores, mochi_id, seo_url, submitter)\
VALUES ('Tesla', 'this is just a description', 'http://juego..swf', 2, 0, 480, 248, 'http://localhsot.jpg', 0, 'swf', 'This are the instructions', '"+ str(now_date) +"', 1, 1, '', 'some-game', 0)"
cursor.execute(query)
Con la función NOW() de MySQL
query = "INSERT INTO games (name, description, url, category_id, category_parent, width, height, image, published, filetype, instructions, date_added, advert_id, highscores, mochi_id, seo_url, submitter)\
VALUES ('Tesla', 'this is just a description', 'http://juego..swf', 2, 0, 480, 248, 'http://localhsot.jpg', 0, 'swf', 'This are the instructions', NOW(), 1, 1, '', 'some-game', 0)"
cursor.execute(query)
Este último utiliza la función de mysql, así que toma la fecha del servidor en donde se encuentre el SMBD.
No olvides hacer el commit para completar la transacción
cursor.execute(query)
db.commit()
db.close()