Get the decoy power-up (TQ09K) then get Robin or Nightwing to put on the technology suit and go to the trophy room. Lay down a decoy then quickly become the decoy, it will die, then you are duplicated!

On the level Penguins lair there is 3 invincible mini penguins. Make sure you have Mr. Freeze. Towards the end there are the three penguins in the room next to the boss battle room (if you don't know how to get there just brake the glass). Take Mr. Freeze and start shooting the penguins with the freeze cannon. This will cause them to freeze. While they are frozen silver cash will pour out of them. When you have the desired amount just beat penguin and cat woman. this works with any other invincible characters.