Each time you defeat Mr. Sinister, you rescue anyone he has captured. Heroes are not considered Bystanders in this case and would not add +1 to Sinister's attack.
The Mastermind is an Enemy and would therefore capture the hero.
The Mastermind is not a Villain and would not get the +2 attack as indicated on the Scheme.
Members of the Henchman and Villain groups are considered Villains.
I wrote this from my memory of the cards, so someone can (and surely will
) correct me if I'm mistaken.