Transport cloning is a type of cloning that will also move an object colliding with the cloned object. The glitch was first discovered by pannenkoek2012 while he was cloning goombas and accidentally displaced a koopa. The technique has had many usages since then, mainly allowing a single HOLP to place many different objects at different locations.
Transport cloning is caused by coding on certain objects that treats how objects collide with each other. The object being pushed (pushee) is the one that needs to be cloned, and will pull the pusher along with it (although the pusher is the one with the code that causes this). The pushee will go to the Y-coordinate of the HOLP, and the average X & Z coordinates between their original location and the HOLP. The pusher only goes to the average X & Z coordinates, while keeping his current Y-coordinate.
Only five different objects can be the pusher- Goomba, Spiny, Wiggler, Koopa (only if he is moving), and Skeeter. The pushee group is a bit more complicated and larger. All of those objects can push any object in Item Group 2- a group composed mainly of bob-ombs, their explosions, and cork boxes. Goomba, Spiny, and Koopa (all items in item Group 5) can also push each other and Lakitu.
Many of the uses for this glitch save time, as constantly having to set HOLP's costs a large deal of time. It also removes the need to continually rebuild a goomba structure as you make it, which is another large time sink.