E-Gate

An E-Gate is a tool used by Luigi to reach places he normally wouldn't be able to reach. The E-Gate functions as a portal as soon as Luigi uses the Strobulb on the green circle on top of it. In a pair, only one can be activated so that they work. The other does not have a green circle, and therefore cannot be activated.

Story
They first appear in the Secret Mine in the mission D-2 "Hit Rock Bottom", where Luigi uses them to his advantage to obtain items and get to various other places. The next and only other time they appear is within the Treacherous Mansion, although here they play a much bigger role. In the mansion, Luigi must use the E-Gates to transport various items to other room so he may progress forward. There are six total E-Gates, all lead to the Front Entrance. There are four on the first floor and two on the second floor. The far left E-Gate leads to the Dark Age Exhibit. The one next to that leads to the Ice Age Exhibit, and has snow around it. The far right E-Gate leads to the Jungle Exhibit, and features vines growing around it. The last one leads to the Ancient Exhibit, and has sand flowing out from it. On the top floor, the left E-Gate leads to the Space Exhibit, while the right can lead either to the Nautical Exhibit or the Study, depending on which way the large compass on the floor of the Nautical Exhibit is facing (north will lead to the Study, while south leads to the Nautical Exhibit).

Trivia

 * The green light on the top will follow Luigi's light. This can result in it clipping through the red ring.