That's what I was thinking, wasn't sure. So do I apply the bonus effects immediately when I fight the mastermind or only if I win? Like some say draw cards or get +3 fight or whatever.
You have to defeat the Mastermind Tactic. Then, after it is defeated, you apply the Fight effect.
The same goes for Villains. Defeat them, place them in your Victory Pile, then resolve the Fight effect.
I assume you're referring to one of Red Skull's Tactics, which tells you to gain +3 ATTACK as the fight effect. You would first defeat it. Then you gain the +3 ATTACK for that turn only. After that turn is over, even if you don't use that ATTACK for anything, it is gone.
The Fight effects always apply to the player defeating the Villain or Mastermind Tactic, Unless it explicitly states otherwise. In a solo game, you are always that player.