There are a few items that change the appearance of the owner. Here are some screenshots of Vayne with various items (note, however, that many of these items are not good to build on Vayne). The Zeke's Harbinger screenshot also includes Soraka as the item requires one extra allied champion to work.
Passive Effect means that the player does not have to do anything to have the visual shown in the image be present. Active Effect means that the player has to manually activate the item to have the visual shown be present (there are additional activatable items in the game not shown here). Passively Activated means that by performing certain actions, the item effect shown will automatically trigger. Note that elixirs are a special case; click on the links to read more about how they work.