The team up fights. Team up with your mentor to face their arch enemy. And it is GLORIOUS.
Kicking Powergirl's butt in the first episode of the Legacy of Krypton arc.
In the first Batman mission against Scarecrow, the boss fight against him consists of fighting many fear based hallucinations. Suddenly, when he prepares to unleash his next swarm... he discovers he's ran out of fear gas. Indeed, you have just proven you don't fear ANYTHING.
If that isn't proof enough for you, wait until later in the game when you go up against the Sinestro Corps. Yellow Lanterns draw their power from Parallax, the DC Universe's physical embodiment of fear. By the time you get to Sinestro himself, you've beaten down dozens of them (and a reprogrammed Manhunter!), and shrugged off enough fear-inducing yellow energy to make Scarecrow's fear-gas attack in Gotham City seem like a fart in an open field in comparison.
The ending movie for the Bludhaven alert. Nightwing is crushed over the fate of his city... but as he says, he's stronger now that he's learned to get back up and continue fighting.
The seventh anniversary event has you fighting against the Anti-Monitor. And you can beat him back. With the aid of the Flash and Reverse Flash, but still...!
Calculator, tired of the Villain Decay the Society has gone through, decides to take matters into his own hands in the "Death of Superman" story line. Turns out that he has Lexcorp employees working for him. And for all we know, Lex doesn't know anything about this.