Dead Effect - Zero Laboratory
Moving backwards when the level starts skips a trigger that sets the door in front of you to lock and dialog to begin. Shooting afterwards attracts the outside zombies towards the door and killing all of the currently spawned zombies will cause a later trigger in the level to progress that allows you to enter the elevator. Normally at the end you would have to kill 3 waves of zombies before the elevator opens. I skip the beginning door locking by killing a zombie that is underneath the door, causing it to stay opened longer and grenade boosting which causes the game to go in slow mo and gives me a good amount of speed to pass it before it closes from walking into the trigger.