Yellow Jacket - blow up the plane with a fire missle in the Junkyard level. Find the crash site and go into the plane, you will find this area inside the plane that has this computer panel. Destroy it to get Yellow Jacket
Warthog - go to the carnival area. Look around. In the hills area, look for a gas can pickup. Destroy the buildings in the area. Look for a homing missle. From the homing missle pick up, look for that hill, and run towards it and the hill will act like a ramp. Brake as soon as your in the air. You will land on a building. Destroy the smaller building and go in the hole it makes. You'll find a small control panel. Destroy it to claim Warthog.
Axel - In the Freeway level, look for the repair station. In that area, look around and you'll find two cranes. One holds a pipe, the other, a cage like item. The cage crane has a yellow cage like box on the left side. To get axel, destroy the yellow box. Aim for the box on the hill with a fire missle. Move around. If you don't make it in one place, aim for the box in another place on the hill. This is tough, aiming for the box is hard, and with cars pounding you from all sides, it's even tougher. I got the shot in fromt the left area of the hill.
ManSlaughter - In the Prison level, after you land on the island, look at the docking area. You whould find a healt pickup somewhere near a bunch of crates. Destroy one of the crates to reveal a ramp. Go up the ramp and get the health. Part of the ship will be near the crates. Fire at that part of the ship. It will reveal a hole. Shoot the lever to reveal Manslaughter.
Minion - Beat the game with everybody.