Here's how I made the obstacles for my own Spy Chasers game.

You'll need a Hot Wheels car or two, aluminum foil, cooking spray, spray paint, and a shitload of hot glue.

1. Wrap aluminum foil around all but one side of the toy car so it makes a mold. You might want to use 2 layers to avoid leaks.
2. Gently remove the car and then deform the foil so it looks more like wreckage.
3. Give the inside of the foil mold a light spray with cooking spray.
4. Melt a whole bunch of hot glue into the foil mold.
5. When it dries and cools, remove it from the foil and wash off any cooking spray residue.
6. Spray paint it blacker than the blackest black times infinity.