Brain Battle was introduced in Destroy All Humans! 2.
Overview[]
Instead of just disguising himself as a human, Crypto could approach one and commence a “Brain Battle” in order to Snatch their body.
During the battle, two beams of red and blue light would be produced: blue represented Crypto's willpower and red represented the human's. If the blue beam broke through, then the Brain Battle was complete and Crypto could successfully inhabit a human body. However, if the red beam managed to resist, then Crypto had to start the Brain Battle all over again.
Crypto had a limited time to be inside of a human body, lasting until their life-force was depleted and their body died, with Crypto bursting out of it unharmed.