Defamation of Character tells an original story in the GTA San Andreas engine. There are several new gameplay features included, most of which are explained in game as they become accessible, but here's the cheat sheet on what does what.

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Bullet Time
What is it: Slow time to half speed to allow for more precise aiming under fire, as well as increasing the gratification of a good kill.
Who can use it: BANMAN only
How do I use it: Simply press Y at any time to go in, and press N to return to normal speed. There is no limit of use on bullet time.
When do I get it: Bullet Time is available as soon as Jack becomes Banman.

Video Demo: 1 2 3

Legal Immunity
What is it: Do whatever you want without fear of police attention.
Who can ue it: JACK THOMPSON only
How do I use it: Kill someone, start a fire, destroy a car, etc...
When do I get it: Legal Immunity is available at the start of the game.

Video Demo: 1 2 3 4 5 6 7

Regenerating Armor
What is it: When you have sustained enough damage, this armor magically replenishes itself after a short delay.
Who can use it: BANMAN only
How do I use it: Take damage, seek cover.
When do I get it: Regenerating Armor is available as soon as Jack becomes Banman.

Video Demo: 1 2

Holy Escort
What is it: Call upon a Higher Power and borrow an invincible harrier jet from God's fleet. As this is God's jet, it automagically transforms into a hovercraft in the event of a water landing.
Who can use it: JACK THOMPSON and BANMAN
How do I use it: Simply face the direction in which you would like the jet to land, and drop a smoke grenade.
When do I get it: Holy Escort is unlocked after the fourth mission, Dam Villian.

 

Video Demo: 1 2

Press Relations
What is it: Hold a press conference and try to perpetuate your wacky personal belief structure through the mass media.
Who can use it: JACK THOMPSON only
How do I use it: When offered a choice between two rhetorical tactics, simply press Y if you wish for Jack to pursue the top choice, and N to select the bottom. Press sprint at any time to advance the dialogue during this event.
When do I get it: This is a one time event which must be completed to pass the third mission, Publicity Stunt.

Video Demo: Press Conference Demo