Sweet~T00TH

You unlock Yellow Jacket in the Junkyard level and it must be one player.

Shoot the plane down with a missle. Follow it to where it crashes (Down in the deepest part of the level) collect the guns and the shoot the control panel.

To get Warthhog go to suburbs, find the ferris wheel and look at the trailers and Find the gas can, then go off the hill land on the first building and if did not, bust the ceiling use a gas can to bust it.

Then shoot the control thing then you unlocked him. This is all I know how to unlock.

DeadWing

Yellow Jacket (Junkyard Level)-shoot the plane that circles the arena. If you hit it with Flame or Homing missiles, it will start on fire. It will descend and crash into the building in the quarry. Go to the wreckage and drive into the hole in the building. You should eventually come to a sewer with a pole/pillar in the middle. Shoot the control panel on this pole. You should get a message saying that you have unlocked Yellow Jacket.

Axel (Freeway Level)-go to the construction yard and aim your vehicle at one of the cranes' control panel. (I forgot which one). When you do, a crane should lower a box into the yard. Destroy the box and you should get a message saying that you have unlocked Axel.

Manslaughter (Prison Passage Level)-wait until the ship has docked. Drive down the ramp to the bottom of the boat. Take a right to the hull (back) of the boat. You should see a stack of crates with a Health Pick Up on top. Shoot the crates (without one-hit kill activated) and they will form a ramp. Drive up the ramp and aim at the boat. Shoot it and a hole should appear. Drive inside and shoot the control panel on the pole/pillar. A message will appear saying that you have unlocked Manslaughter.

Warthog (Suburbs Level)-go to the carnival where the Ferris Wheel is. Turn around and you should see a bank with a gas can power up on it. (It is to the right of the hill leading back down to town). Aime yourself at the power-up and jump of the bank. You should land on top of one of the factories. Shoot the raised section of the roof and drop inside the formed hole. Shoot the control panel inside and a message should appear saying you have unlocked Warthog.

Minion-you must complete story mode with all of the characters. (original and unlockable) You will get a message saying 'Beware of Minion'. You can now play as him.