Lightning Shadow (電影 Den'ei, literally means "Virtual") is a keyword ability that was introduced in Booster 32: Code:Dreamworld - Dreamclad "Idealize". It is associated with the "Shaddow".
This ability essentially allow a player to "exchange" one of their Reboot State Z/X on Square with a Z/X that possessed Lightning Shadow in their hand as long as the Cost of that Z/X is equal to or greater than the number inscribed in the Lightning Shadow ability. In doing so, that player is unable to play another Lightning Shadow ability during that turn.
The current reminder text of Lightning Shadow ability is shown below:
電影Ｘ（ 手札 スクエアにあるあなたのコストＸ以上のリブートのゼクスを１枚手札に戻す。 このカードをリブートでそのゼクスがあったゼクスのないスクエアに登場させる。ターン終了時まで、あなたは“ 電影”をプレイできない。）
[Boot] Lightning Shadow X ( <Valid> [Own Turn] Hand <Cost> Return one of your Cost X or greater Reboot State Z/X on Square to hand. <Effect> Make this card appear on Square without Z/X that had that Z/X before in Reboot State. Until end of turn, you cannot play " [Boot] Lightning Shadow".)
For the list of all cards with Lightning Shadow ability, see Category:Lightning Shadow.