In the Snowy Toronto stage, fight your way to Hillcrest Park. Without killing the last enemy before you're allowed to move on, move over to the middle of the right side of the screen and hold up and right. You'll see your character slowly start to move off screen, after which you can dash blindly through the level with none of the enemies loaded. After the screen dips down and back up, hold up and right to make sure you enter the Subspace door at the end of the level. This is a great way to earn the Invulnerable trophy with very little effort.