The animated events that happen on the map such train exploding or train crashing, if you stand totally still you will not be killed during the animation and once the animation is finished you can attempt to move again. However if you are completely overlapped by the train you get stuck inside of it.
This can also be used via revives to cause you to dsync meaning you can walk around the map and be invisible as your body stays in the train.
Biggest problem is you can still call in lasers, arty strikes and lay down placeable objects (such as turrets) while in this ghost mode. Allowing you to put turrets behind their spawns and stuff.
