Go to the first level, The Training Level, Go GHOST and find the room where you and Lambert have a conversation, if you found it, if out the room you will see a door with keypad press 7393 or go GHOST you can kill Lambert (No message of mission failure), you can kill your twin, err, YourSelf, kill your twin, he is still standing, there is an interaction if you don't kill your twin first "GRAB CHARACTER". Killed (but still standing even shooting him much times), the interaction is "BODY". Carry him, they both will do it together, then Tada THE TWIN OF EVIL!